Avionics upgrade wiring questions

[PHILIP GUZIEC]

Hi all.

Unfortunately, the GX60 In my mooney can no longer be updated and I'm being forced into an upgrade cycle. I'm trying to contain the cost of the whole thing But of course the avionics chops want me to rip everything out and sell every upgrade So, some tactical questions.

My current setup is a century attitude indicator and HSI that drive a century 2000 auto pilot. The input to those is a switch and a nunciator between the GX60 and A king nav with glideslope..

What I'd like to do is ditch my tailbeacon and put in a garmin 375 in the same place is the GX60 And replace my DME with an old king com that I have on the shelf. One shop I talk to tells me that I can't use the existing annunciator switch for the output of the 375 and the nav to the hsi and autopilot.

My 1st question is whether it is true that I can't use the existing annunciator switch. It seems like it would be a paperwork issue rather than an actual functional issue if the existing switch can't be used.

If in fact I can't use the existing switch I would wire the 375 directly into the HSI and the auto pilot. I have one localizer indicator without glideslope in the panel and I have a king localizer indicator with a glidelope on the shelf. I'm pretty familiar with automotive stuff but I'm not familiar with how things are done on airplanes and what's legal. Does anyone know if the king indicator connectors typically are the same between the units with or without glideslope so that wires and pins can be slipped in and added?

Another general question. I see units of different types ibeing sold with trays with wire pigtails. Is it legal to spilce wires in avionics? Is this typically done with a connector or solder and heat shrink?

Thanks for any advice!

 

[asicer]

My 1st question is whether it is true that I can't use the existing annunciator switch. It seems like it would be a paperwork issue rather than an actual functional issue if the existing switch can't be used.

Figure B-6 of the GNX375 installation manual shows a relay to allow 2 sources to drive 1 indicator so it is possible. However, there could be any number of reasons your shop doesn't want to sign off on that.

Does anyone know if the king indicator connectors typically are the same between the units with or without glideslope so that wires and pins can be slipped in and added?

Model/part numbers would help.

 

[PHILIP GUZIEC]

Figure B-6 of the GNX375 installation manual shows a relay to allow 2 sources to drive 1 indicator so it is possible. However, there could be any number of reasons your shop doesn't want to sign off on that.

Model/part numbers would help.

Thanks for the response. Can you direct me to where I can find the install manuals for the 375 to which you are referring?

My currently wired switched input works perfectly, and has a ILS gps lockout. The shop suggested there is a specific switch needed for the 375 different from the current one.

I'll put together the part numbers but here's a pic. The nav is a 53 TSO. I need to look up the part numbers of the indicator installed, the one on the shelf, and the switch installed with the GX60. I'll report back.

While we're at it though, how is splicing typically done on aircraft?

 

[Chip Sylverne]

I replaced a GX50 with a 175, so the installation is very similar. You probably have the Apollo ACU switch? Your shop is correct, that one can't be used, not enough poles. However, you can use some of that existing wiring to your HSI by installing a D sub connector to the former output harness of the ACU. The proper size and type connector is available from Mouser.com. saves a lot of work. I opted to dedicated the 175 to the HSI, and the second VOR/GS dedicated to a nav. It wasn't worth the trouble and expense of finding a 14v relay to do the switching. Pretty much all approaches are available as a GPS with vertical guidance, or as overlays anyway. Not having an ILS available to the HSI hasn't been a problem.

There are a ton of resources on the web about how to properly do aircraft wiring. Most splicing is done with crimp pins and sockets. Solder sleeves are also the cat's ass. AC 43.13 and the NASA guide are the most helpful. If you plan to do this under the guidance of your A&P, be prepared to spend some cash on tools.

 

[Bell206]

I see units of different types ibeing sold with trays with wire pigtails. Is it legal to spilce wires in avionics?

Yes its legal in most situations but there can be exceptions. The most common and preferred method to splice is to use a Raychem crimp or solder splice. However, if you are looking to purchase pre-wired trays with your equipment just have the vendor cut the wires to your required lengths. Then you only have to terminate the wires vs splice them which is not the best way to do things especially a new install.

 

[PHILIP GUZIEC]

Thanks!

I'd love to do it under supervision but my main interest is to know exactly what I want when I get the push to just dump in a new 30k stack.

Attached is an image of the annunciator. Not sure if the relay is a set Or how many poles.

The auto pilot follows whatever is on the HSI. Is that typically switched in parallel or is there a signal split on an output from the HSI or relay?

I'm fine dedicating the hsi and autopilot to the new GPS. Unfortunately second nav doesn't have glideslope.but that might not be a big deal. I can either Install the indicator with the glideslope that I already have and wire it to nav 1 and remove nav2 or just leav the lateral only in place as a backup. I just don't like the idea of having nothing if GPS goes down.

Attached is an image of the switch annunciator?

 

[Chip Sylverne]

That's not the Apollo ACU with integral switch, that's just an annunciator, so whatever relay that's controlling is what matters. If you look in the 375 install manual, the only annunciators required if the GPS isn't in field of view are two lamps : a GPS and a Nav. If your relay has sufficient poles, you could drive that with a simple 2 position Eaton switch. You need the p/n off the relay to know for sure. I'd have to dig up my install notes to tell you the number of poles required. 14 comes to mind, but I wouldn't bet on bet on it.

The relay switches in parallel, the hsi will be driven either by the nav output or the GPS output. The a/p follows the HSI needles, it doesn't care what the source is.

 

[PHILIP GUZIEC]

That's great, so the HSI has an output that drives the autopilot?

This all gives me some background to start digging around in my documentation.

The 175 would be the cheapest way to go. I do wonder if this isn't the time to get official ADSB in with the 375 as I can still sell the tailbeacon and then there is no additional mounting issues. If I add displays to the panel later, I will have a driver for them. Any thoughts?

 

[asicer]

I do wonder if this isn't the time to get official ADSB in with the 375 as I can still sell the tailbeacon and then there is no additional mounting issues. If I add displays to the panel later, I will have a driver for them. Any thoughts?

What’s the price delta? How much do you think you can get for the tailBeacon? What’s your plan if the KT76 lunches after installing a 175?

 

[WDD]

Penny wise pound foolish, or something like that. IMHO get the 375, sell the tail beacon, and let the KT76 rest in peace.

Keeping the plane for a long time? Maybe think about what life would be like with a GTX 345 and a GTN 650 xi.

 

[Chip Sylverne]

That's great, so the HSI has an output that drives the autopilot?

This all gives me some background to start digging around in my documentation.

The 175 would be the cheapest way to go. I do wonder if this isn't the time to get official ADSB in with the 375 as I can still sell the tailbeacon and then there is no additional mounting issues. If I add displays to the panel later, I will have a driver for them. Any thoughts?

It's not so much that the HSI sends signals, it's that the a/p uses the L/R up/down excitation voltage the nav or GPS sends to the HSI in parallel by splicing into those wires.
ADS-B in is worth it's weight in gold as far as I'm concerned. Traffic has saved my ass a couple times. The only reason I went with the 175 is because I had ADS-B in already, an MFD display and a couple SL30 nav/coms.

 

[PHILIP GUZIEC]

What’s the price delta? How much do you think you can get for the tailBeacon? What’s your plan if the KT76 lunches after installing a 175?

Say the price delta is 3 grand including selling the tailbeacon and new encoder. I have two spare 76s on the shelf. I do have a stratux already with two yoke mounted iPad minis that give me traffic and weather. However, I like the elegance of the transponder integrated with the GPS so no wiring and the relatively infrequently updated transponder code rather than a com.

 

[PHILIP GUZIEC]

Penny wise pound foolish, or something like that. IMHO get the 375, sell the tail beacon, and let the KT76 rest in peace.

Keeping the plane for a long time? Maybe think about what life would be like with a GTX 345 and a GTN 650 xi.

What does 650 really buy me besides a bigger screen?

 

[PHILIP GUZIEC]

It's not so much that the HSI sends signals, it's that the a/p uses the L/R up/down excitation voltage the nav or GPS sends to the HSI in parallel by splicing into those wires.
ADS-B in is worth it's weight in gold as far as I'm concerned. Traffic has saved my *** a couple times. The only reason I went with the 175 is because I had ADS-B in already, an MFD display and a couple SL30 nav/coms.

Thanks. Exactly what I wanted to know about a split signal. So I could just take the output signal of the gps directly into the current output wiring of the relay if o ditch the legacy nav.

 

[WDD]

What does 650 really buy me besides a bigger screen?

1) bigger screen is nice
2) a modern nav com, with the auto loading nav into standby when you load an ILS approach. It will also easily switch from VOR to GPS. There is a reason it’s a standard

 

[Chip Sylverne]

Thanks. Exactly what I wanted to know about a split signal. So I could just take the output signal of the gps directly into the current output wiring of the relay if o ditch the legacy nav.

Little more complicated than that, and you'll need the pinouts and wiring diagrams for each piece of equipment, but that's essentially the gist of what I did. Grab an install manual for the GX, and reverse engineer.

 

[PHILIP GUZIEC]

1) bigger screen is nice
2) a modern nav com, with the auto loading nav into standby when you load an ILS approach. It will also easily switch from VOR to GPS. There is a reason it’s a standard

I think I'm hearing that everyone shoots GPS approaches about 99 percent of the time? No?

 

[WDD]

Mostly. Although where I fly a lot of airports have ILS as well. And you’ll need that capability anyway to take your IR checkride. (I think you would have that capability if you paid to install your old king glide slope and old king nav com ???).

While the 650xi and GTX 345 combo would simplify things as well a provide an updated com and nav radio, the 375 is also a great choice from what I’ve read. And would cost much less.

 

[PHILIP GUZIEC]

Mostly. Although where I fly a lot of airports have ILS as well. And you’ll need that capability anyway to take your IR checkride. (I think you would have that capability if you paid to install your old king glide slope and old king nav com ???).

While the 650xi and GTX 345 combo would simplify things as well a provide an updated com and nav radio, the 375 is also a great choice from what I’ve read. And would cost much less.

Thanks. I'm already instrument rated With about 7:50 hours flying all over The US and Caribbean. I've been flying much less Since having kids and no actual in years. I used the GX60 from point to point but never shot a GPS approach in actual. Now I hear there are GPS overlays for just about every Ils So the nap is just a backup against GPS failing. I currently have a backup a nav without a glideslope But I also picked up a gs indicator that I work with my primary nav. If the existing relay will work with the 375, I'll wire it that way. If not, the question is whether to just leave the backup nav with lateral guidance or spring for a new relay for the old one to the HSI or install the indicator with hlideslope I already have on the shelf.

 

[asicer]

I think I'm hearing that everyone shoots GPS approaches about 99 percent of the time? No?

Not 99% but a lot. There's a few airports where the RNAV IAF is on the wrong side while the VOR approach is aligned with my route of flight.

 

[asicer]

If the existing relay will work with the 375, I'll wire it that way. If not, the question is whether to just leave the backup nav with lateral guidance or spring for a new relay for the old one to the HSI or install the indicator with hlideslope I already have on the shelf.

I'd just install the CDI that has the GS. If it's a backup, best to have it as separate from the main system as possible.

 

[WDD]

https://www.ifr-magazine.com/charts-plates/ils-on-the-block/

 

[Chip Sylverne]

I checked my install notes and the relay required to switch HSI driver between the nav and gps was a Mid Continent MD 41-244 24 pole ( 3 poles per connector) . Very spendy at $1,400 new and hard to find at 14v, so I bagged it. But if that's what you currently have installed...

I used a DB9 connector to connect the GPS resolver outputs to the HSI rather than solder splices, and for annunciator connections. The thing that screws you using your current annunciator is there's no LOI (loss of integrity) lamp.

 

[PHILIP GUZIEC]

Thanks for looking that up. I'll report back with what I have installed and which way I can go. If the GPS is in the stack to the immediate right and there is a nav/gs flag on the HSI, is a LOI light required? Could I ditch the annunciator and just use a simple switch?

I'm actually considering leaving in the GX60 for the Com since I don't have a tray for my spare com and it won't require any more work.

If I have the right relay, I'll leave the setup as is with an acceptable switch. If not, it will either be a new tray for my spare 197 com or leave in the GX 60 for the com, and wire or move the Nav/GS and install that indicator.

 

[flyingcheesehead]

Generally, wiring up whatever you get is the most expensive part of an avionics upgrade, so you might as well spend a little extra for a lot more capability in most cases.

Making new stuff work with old also costs more. Of course, if we could have everything we wanted, we'd probably be buying new airplanes instead of tinkering with used ones, but the point remains - Spring for what you want to the extent possible. The 375 is a really nice unit and gives you a lot of new capabilities (WAAS, color screen, ADS-B, etc) in one handy box.

I have two spare 76s on the shelf.

Keep in mind, a KT-76 is probably full of electrolytic capacitors that are already leaking, unless you've had them re-capped already. Once the electrolyte eats through traces on the board, it's a goner. So, you may well find that once the KT-76 in your panel gives up the ghost, that the ones you have on the shelf are also bad as well.

A 375 is an excellent option.

 

[Chip Sylverne]

Thanks for looking that up. I'll report back with what I have installed and which way I can go. If the GPS is in the stack to the immediate right and there is a nav/gs flag on the HSI, is a LOI light required? Could I ditch the annunciator and just use a simple switch?

I'm actually considering leaving in the GX60 for the Com since I don't have a tray for my spare com and it won't require any more work.

If I have the right relay, I'll leave the setup as is with an acceptable switch. If not, it will either be a new tray for my spare 197 com or leave in the GX 60 for the com, and wire or move the Nav/GS and install that indicator.

Yes, you could use a simple switch. As far as field of vision goes, specs are in the install manual, and quite frankly your A&P/IA has some discretion in making that call. Really though, the requirement for two lamps, APPCH and LOI couldn't be simpler. All it takes is a 1 amp breaker, a couple light sockets and a label.

 

[Papa Pilot]

Disclaimer: Plane owner who has done a series of avionics upgrades in my plane under IA supervision over the last 4 years or so. I am not an avionics professional.

Random bits of advice I have to offer.

• Yes, the wiring is the most time intensive piece of work. I estimate how long it takes then multiply by three.
• As a general rule I don't splice pigtails that have been cut. For D-sub connectors get a pin removal tool, a pin crimper, some pins and start anew. Less labor, cleaner install, and IMO more reliable connections. (If you'll be doing further upgrades you'll need these tools anyway.)
• Some older boxes don't use D-subs so removing pins aren't as easy. You can find older style connectors and pins and start anew if you want to go that route. If you can't find new or don't want to go that route splicing is fine.
  
• If buying used, you may have to buy your own connectors. Most modern avionics use D-sub connectors that can be sourced from various places. I've found, however, that if I need a metal shell, mouser.com is the place to go. Also keep in mind D-subs use two different pin sizes. Get the right size.
• Study all the install manuals of the avionics you'll be installing or connecting to. Map out how things will be connected and what pins will used for each box before you cut the first wire.
• When you do start making the harnesses and connections, go slow and be conscientious. The work is not difficult; it's detailed, meticulous, tedious, and time-consuming. If that's not your cup of tea, don't do it.
• Work in chunks and complete the chunk before moving to the next one.
• Incrementally test as you wire things up. You don't want to have everything bundled up and then discover you pinned something wrong.
• Tripple and quadruple check you've made the right connection.
• Those funky looking binocular magnifiers ... (Amazon.com: Headband Magnifier, Professional Double Lens Head-Mounted Loupe Jewelry Magnifier, Reading Visor Opitcal Glass Binocular Magnifier with Lens Magnification-1.5X 2X 2.5X 3.5X for Repair, Crafts : Health & Household) Get a pair. Your eyes will thank you.
• Don't underestimate what it will take to mount the trays. Even if you're installing only one new box, you may have to do some major rearranging of the existing boxes and that may mean making new brackets.
• I just replaced my GX50 with a waas unit and needed to use a different annunciator. Waas units have different requirements - Check the requirements in the install manual.
• Your new waas GPS will require a new antenna. You'll probably need to take the interior and headliner out to get to the old antenna. Make time for that.
• You haven't mentioned what audio panel you have. Is it up to snuff? If not, a modern audio panel should be seriously considered. It is a chore to install and will triple your down time. But in the end, it is time and effort well spent. Been there, done that, very happy I did it.
  
• Given your scenario, I'd go with the GNX 375. Slightly more than a used 430W but you'll be able to ditch your old transponder (good) and tail beacon but gain waas navigation and ADS-B in. The GNX will also be supported for some time. Dedicate the GPS to your HSI. Get another NavCom with GS and an appropriate indicator for ILS approaches. With this setup you'll have two completely separate navigation systems: one spaced based and one terrestrial. (something I prefer, but YMMV) The one caveat is that your terrestrial nav system won't be able to drive the autopilot, but I don't see this is a huge loss of functionality. Additionally, with this set up, you won't have to worry about wiring up relays to swap the display, so that can all be yanked as well.

OK, I'm tired of typing. Drop me a personal message if you want. Happy to share what I've done.

 

[PHILIP GUZIEC]

Disclaimer: Plane owner who has done a series of avionics upgrades in my plane under IA supervision over the last 4 years or so. I am not an avionics professional.

Random bits of advice I have to offer.

• Yes, the wiring is the most time intensive piece of work. I estimate how long it takes then multiply by three.
• As a general rule I don't splice pigtails that have been cut. For D-sub connectors get a pin removal tool, a pin crimper, some pins and start anew. Less labor, cleaner install, and IMO more reliable connections. (If you'll be doing further upgrades you'll need these tools anyway.)
• Some older boxes don't use D-subs so removing pins aren't as easy. You can find older style connectors and pins and start anew if you want to go that route. If you can't find new or don't want to go that route splicing is fine.
  
• If buying used, you may have to buy your own connectors. Most modern avionics use D-sub connectors that can be sourced from various places. I've found, however, that if I need a metal shell, mouser.com is the place to go. Also keep in mind D-subs use two different pin sizes. Get the right size.
• Study all the install manuals of the avionics you'll be installing or connecting to. Map out how things will be connected and what pins will used for each box before you cut the first wire.
• When you do start making the harnesses and connections, go slow and be conscientious. The work is not difficult; it's detailed, meticulous, tedious, and time-consuming. If that's not your cup of tea, don't do it.
• Work in chunks and complete the chunk before moving to the next one.
• Incrementally test as you wire things up. You don't want to have everything bundled up and then discover you pinned something wrong.
• Tripple and quadruple check you've made the right connection.
• Those funky looking binocular magnifiers ... (Amazon.com: Headband Magnifier, Professional Double Lens Head-Mounted Loupe Jewelry Magnifier, Reading Visor Opitcal Glass Binocular Magnifier with Lens Magnification-1.5X 2X 2.5X 3.5X for Repair, Crafts : Health & Household) Get a pair. Your eyes will thank you.
• Don't underestimate what it will take to mount the trays. Even if you're installing only one new box, you may have to do some major rearranging of the existing boxes and that may mean making new brackets.
• I just replaced my GX50 with a waas unit and needed to use a different annunciator. Waas units have different requirements - Check the requirements in the install manual.
• Your new waas GPS will require a new antenna. You'll probably need to take the interior and headliner out to get to the old antenna. Make time for that.
• You haven't mentioned what audio panel you have. Is it up to snuff? If not, a modern audio panel should be seriously considered. It is a chore to install and will triple your down time. But in the end, it is time and effort well spent. Been there, done that, very happy I did it.
  
• Given your scenario, I'd go with the GNX 375. Slightly more than a used 430W but you'll be able to ditch your old transponder (good) and tail beacon but gain waas navigation and ADS-B in. The GNX will also be supported for some time. Dedicate the GPS to your HSI. Get another NavCom with GS and an appropriate indicator for ILS approaches. With this setup you'll have two completely separate navigation systems: one spaced based and one terrestrial. (something I prefer, but YMMV) The one caveat is that your terrestrial nav system won't be able to drive the autopilot, but I don't see this is a huge loss of functionality. Additionally, with this set up, you won't have to worry about wiring up relays to swap the display, so that can all be yanked as well.

OK, I'm tired of typing. Drop me a personal message if you want. Happy to share what I've done.

Thanks for taking the time to type this out. Exactly the kind of detail I was looking for. Your suggestion is exactly what I had converged on doing. The 375 will be the only modern piece, and nice that no wiring to the transponder. I can always add a modern display later, but I have spare AI and HSI on the shelf/

Is there a good online source for install manuals that I can look at before purchase?

I found a third 97 with a tray for the price of a tray, so that will replace the DME as COM2 without moving anything else in the stack. Existing power wires there and the radio outputs to the audio panel and antenna from the GX60. I plan to send them to kx155.com for a checkout and will have a spare on the shelf.

Looks like I found an indicator with glideslope, so I'll wire that directly from the current NAV in the center stack and remove the old localizer only nav and indicator (it's actually a glideslope radio too so I'll have a spare on the shelf). Power and audio won't need to change, and I should only need to add a couple of new wires. I bought a pin remover set with about 50 options a number of years ago. Been very handy. Maybe new pins on the end of old wires as close as they are located.

I'll dedicate the GPS to the HSI and autopilot which, I agree, isn't much of a loss over switching. Existing power wire from the GX60.

Not many ILS systems without GPS overlay. I'll also retain the Stratux and dual ipad minis so I'll have redundant GPS backup and Nav in.

Ideally, I'd like to have a shop do it, but I wanted to identify a minimal effort install and a sense of the effort before walking in to the shop. Not looking to do a 50k avionics upgrade here. Seems like much of it can be done by re-pinning the outputs of old wires. New radios fill old slot sizes.

Too bad the old GPS antenna wire standard is different than the new or I could just swap antennas rather than rewiring and pulling the headliner.

 

[edessa]

A friend of mine did a gut job on his 1964 Mooney. Here the before and after. No autopilot yet. It's only money.

 

[Chip Sylverne]

Thanks for taking the time to type this out. Exactly the kind of detail I was looking for. Your suggestion is exactly what I had converged on doing. The 375 will be the only modern piece, and nice that no wiring to the transponder. I can always add a modern display later, but I have spare AI and HSI on the shelf/

Is there a good online source for install manuals that I can look at before purchase?

I found a third 97 with a tray for the price of a tray, so that will replace the DME as COM2 without moving anything else in the stack. Existing power wires there and the radio outputs to the audio panel and antenna from the GX60. I plan to send them to kx155.com for a checkout and will have a spare on the shelf.

Looks like I found an indicator with glideslope, so I'll wire that directly from the current NAV in the center stack and remove the old localizer only nav and indicator (it's actually a glideslope radio too so I'll have a spare on the shelf). Power and audio won't need to change, and I should only need to add a couple of new wires. I bought a pin remover set with about 50 options a number of years ago. Been very handy. Maybe new pins on the end of old wires as close as they are located.

I'll dedicate the GPS to the HSI and autopilot which, I agree, isn't much of a loss over switching. Existing power wire from the GX60.

Not many ILS systems without GPS overlay. I'll also retain the Stratux and dual ipad minis so I'll have redundant GPS backup and Nav in.

Ideally, I'd like to have a shop do it, but I wanted to identify a minimal effort install and a sense of the effort before walking in to the shop. Not looking to do a 50k avionics upgrade here. Seems like much of it can be done by re-pinning the outputs of old wires. New radios fill old slot sizes.

Too bad the old GPS antenna wire standard is different than the new or I could just swap antennas rather than rewiring and pulling the headliner.

I can help you out with the GPS stuff. Shoot me a PM with a real email addy

 

[Llk]

Philip,

Pm me and i can help you with all the manuals.

I ditched a few gx60’s and despise garmin for their support policy. If I can pay money to someone else I do.

The 375 works, but since you have used stuff, you have alternatives, some current and others no longer supported.

Hit me up.


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