PA-28R Dim Gear Light

iamtheari

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In my Piper Arrow (the original Hershey bar wing, 180hp version), the left main gear indicator light is dim, maybe 1/4 the intensity of the other two lights. Moving the bulbs around keeps the dim light at the left main position. Turning on the nav lights dims all three indicators further, so I don't think it's somehow failing to undim the left main light. I have not noticed any flicker or other weirdness.

Other than pulling all new wires to diagnose with my checkbook, does anyone have suggestions for causes to rule out?
 
corrosion in the left main bulb housing?
Could be. I suppose the way to rule that out is a multimeter at the housing to check if there's 12V at that point with the master switch on, and to compare resistance to the other two housings with the master switch off.
 
Could be. I suppose the way to rule that out is a multimeter at the housing to check if there's 12V at that point with the master switch on, and to compare resistance to the other two housings with the master switch off.

First step would be to clean the metal contacts in the dim light circuit, and look for corrosion in the connections to that bulb. It is too easy to get a false resistance/voltage measurement when your contact is the pointy end of the multimeter probe. -Skip
 
First step would be to clean the metal contacts in the dim light circuit, and look for corrosion in the connections to that bulb. It is too easy to get a false resistance/voltage measurement when your contact is the pointy end of the multimeter probe. -Skip
I trust my multimeter more than my eyes. My theory is that, if the multimeter shows full voltage at the socket, it means that the socket is the problem and I have ruled out the rest of the circuit (wire and microswitch). But I will also try to look in the socket for corrosion or other contamination and give it a squirt of contact cleaner for good measure.
 
I trust my multimeter more than my eyes. My theory is that, if the multimeter shows full voltage at the socket, it means that the socket is the problem and I have ruled out the rest of the circuit (wire and microswitch). But I will also try to look in the socket for corrosion or other contamination and give it a squirt of contact cleaner for good measure.

Skip has a point, although the way he wrote it may be too subtle unless you’re pretty familiar with electricity and troubleshooting. Unless you test the full functioning circuit full voltage at the socket may not mean much since there is no load.
 
Skip has a point, although the way he wrote it may be too subtle unless you’re pretty familiar with electricity and troubleshooting. Unless you test the full functioning circuit full voltage at the socket may not mean much since there is no load.
Good point, thanks. I'm mostly trying to find objective metrics I can use to rule out likely causes without needing an expert eye to make subjective judgment calls.
 
try a simple application of contact cleaner.
 
Get the maintenance manual for your aircraft . Find the correct wiring diagrams for your serial number. Figure out the possible places that could cause a poor connection, starting from easiest to check and most likely.

My money is on a connector or switch that comes in contact with wind, moisture, etc. Wheel well, gear leg, cowling. As I recall, those switches are pretty Mickey Mouse affairs.

Might be best to jack the aircraft for safety before touching. Don't want to wear the piper.
 
In my Piper Arrow (the original Hershey bar wing, 180hp version), the left main gear indicator light is dim, maybe 1/4 the intensity of the other two lights. Moving the bulbs around keeps the dim light at the left main position. Turning on the nav lights dims all three indicators further, so I don't think it's somehow failing to undim the left main light. I have not noticed any flicker or other weirdness.

Other than pulling all new wires to diagnose with my checkbook, does anyone have suggestions for causes to rule out?

Has it always been that way. Or did it just start doing that? If you adjust the panel dimmer does it change it's intensity at all?
 
Has it always been that way. Or did it just start doing that? If you adjust the panel dimmer does it change it's intensity at all?
It started suddenly, but not recently. See my earlier 2017 thread that @Spring Ford found. Same thing, I just haven't figured it out yet. The panel dimmer has no effect on it, other than the fact it dims proportionally with the other two lights in the well-known Piper Arrow "crap my gear isn't going down!" effect of turning on the nav lights. That is, all three lights have two settings. High and low. And the affected one is also both high and low, but both settings are much dimmer than its neighbors.
 
On second thoughts. I have been having a quick look at the schematics for some random PA-28R.

Under NO CIRCUMSTANCES troubleshoot this with the electrical system live.

One wrong move and the gear could retract.

The indication system is of course intimately bound with the actuation system

You should probably leave this to a professional.
 
It started suddenly, but not recently. See my earlier 2017 thread that @Spring Ford found. Same thing, I just haven't figured it out yet. The panel dimmer has no effect on it, other than the fact it dims proportionally with the other two lights in the well-known Piper Arrow "crap my gear isn't going down!" effect of turning on the nav lights. That is, all three lights have two settings. High and low. And the affected one is also both high and low, but both settings are much dimmer than its neighbors.

Gotcha. It isn’t what I thought it might have been then. Good luck tracking it down soon.
 
Contact cleaner and insert/remove bulb a half dozen times seems to make it shine equal to the other two lights when the panel lights are off. When they are on, it still looks dimmer (as in the other two are barely visible and the problem bulb appears off), but that's in a lit hangar. Once the annual is done, I'll have to fly with it during the day and night a bit to see if there is a real improvement or not.
 
Since you swapped bulbs, and the problem stays with the left main bulb, I suggest that the left main "down lock" switch could be bad resulting in a high resistance circuit from the 12 volt bus to the bulb. The microswitches for the gear are sealed but they do age (like all of us). You might check that BUT, as the OP stated, do it with the plane on jacks just to be safe!! upload_2019-6-17_17-59-6.png
 
Since you swapped bulbs, and the problem stays with the left main bulb, I suggest that the left main "down lock" switch could be bad resulting in a high resistance circuit from the 12 volt bus to the bulb. The microswitches for the gear are sealed but they do age (like all of us). You might check that BUT, as the OP stated, do it with the plane on jacks just to be safe!!
Thanks for the diagram. Is the ground on the bottom of that diagram (through the resistor) or the top? If I were designing it, I would put it at the top and ground the switches to a common point in the wings to save on wire weight.

My thought now is that, assuming the contact cleaner did not fix the issue, I can measure the resistance from the bulb socket to ground, a path which would be nothing but wire and one switch, and compare the left main to the right main and nose. Since the light has been consistently dim, not flickering (at least not flickering slowly enough for the eye to discern), this should at least narrow it down to the side of the circuit between the bulb and ground. And that's something I can easily test in the plane with the master switch off. No need for jacks.

If I narrow it down to the switch, I can write it up for my next annual so it can be done when the plane is already on jacks.
 
Yes, I agree with your plan. The "low side" connection of the socket is through a fixed resistor when nav lights are ON or direct to ground via the nav light switch if nav lights are off thus making the lights dim when nav lights are on.
 
Yes, I agree with your plan. The "low side" connection of the socket is through a fixed resistor when nav lights are ON or direct to ground via the nav light switch if nav lights are off thus making the lights dim when nav lights are on.
So, I had it backwards and the switches connect to positive voltage on their common terminals, which complicates things slightly. But it's still a workable plan. And I am thinking about changing out or short-circuiting that stupid resistor while I'm at it...I wonder if I can find an IA to sign off on that. I've never been landing at night and thought to myself "I am sure glad those gear indicator lights are extremely dim, that really inspires confidence!"

But basically I can leave the panel light switch off and test the following resistances:

A - Left neg to ground: should be close to 0
B - Right neg to ground: should be close to 0
C - Nose neg to ground: should be close to 0

D - Left to nose: should be close to 0
E - Left to right: should be close to 0
F - Nose to right: should be close to 0

If A, B, C, and F are all 0 and both D and E are significantly above 0 and similar to each other, then I will have isolated the problem to the left main switch and its wiring. If all of these are indeed close to 0, then the bulb socket is the most likely culprit. (Although I really do suspect the switch since it lives out in the elements, gets an oily bath if the strut leaks fluid, and otherwise has probably had a much rougher life than the bulb socket over the past 50 years.)

It looks like switches are reasonably priced in airplane terms:
https://www.knots2u.net/switch-down-limit-main-gear-piper-67411-04-67411-004/
 
Agreed although it might also be the "handshake" connector for the downlock switch wiring. Located on the gear itself. You might check that too. It is usually covered with some type of plastic tubing that protects the connector but I suppose it could have become corroded, etc.
 
I finally got around to measuring the resistances. All three bulb socket negative sides measure 0.1 ohm or less resistance between each other. The nose and right bulb socket positive sides measure low or no resistance between each other. The positive side of the left bulb socket measures 220 ohms to either of the other two bulb sockets. So the bulb and socket are eliminated from contention, and we can say with certainty that the problem is in the positive side of the circuit for the left bulb. Next step might be to soak the switch down in contact cleaner and go up to cycle the gear a few times.

Agreed although it might also be the "handshake" connector for the downlock switch wiring. Located on the gear itself. You might check that too. It is usually covered with some type of plastic tubing that protects the connector but I suppose it could have become corroded, etc.
What is the ‘handshake’ connector?
 
The "handshake" connector looks kind of like a pair of scissors in that the two ends close down on each other. They are used on the gear switches on my Arrow and are covered with clear tubing the ends of which are tied tightly to keep (or minimize) moisture, grease, etc.

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I'm having the same problem except it's the nose wheel light that is very dim. Did you find the problem with yours? Thanks! 1969 PA-28r-180
 
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I'm having the same problem except it's the nose wheel light that is very dim. Did you find the problem with yours? Thanks! 1969 PA-28r-180
No solution yet. I did spray the switch with contact cleaner before my last flight, no improvement. I'll do that a few more times before I give up and order a new switch.
 
Thanks Iamtheart, If you find something, Please post it, and I'll do the same thing. I've also sprayed the socket and it didn't make any difference. The nut on back of the socket is loose, but the other day I didn't have anything to tighten it up with. I hope to trouble shoot it more this Sunday and Monday. Best of Luck!
 
Hey Iamtheari, I posted on Facebook PA-28 page and got a couple of responses that I've copy and pasted here, Maybe this will help us both: From A.S. Had this happen to me, with the light getting dimmer and dimmer over time. Problem went away when we replaced the gear switch. From L.Hunt,, Had the same problem. Retract the gear and right gear light would stay on but would be dim. A&P tried to clean the switch but this last annual had it replaced. No more problem. I guess I'll try and get a new switch
and have it replaced this week.
 
Circling back to close the loop on my old thread, because I hate Googling for a problem and finding nothing but unsolved mysteries. The switch was indeed the problem here. There was a butt splice rather than handshake connector on this particular plane but that won't be hard to replace. Thanks to everyone who replied.
 
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