PA-28R Gear Indicator Light Dim - not bulb

iamtheari

iamtheari

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Ari
The left main gear indicator in my Arrow is dim. I swapped the bulb between the left and right sides and it is still the left one that is dim. I haven't tried swapping the green lens that the bulb goes into. What are the other likely culprits?
 
Just don't start throwing parts at it to fix it. Take a voltmeter from the aircraft parts section of Harbor Freight. Measure the voltage to ground from both left and right bulbs AT THE BASE OF THE SOCKET where the bulb is inserted. They should differ, right being higher than left (1). If they are the same, then measure from the "ground" of the socket to a real airframe ground. They should differ, the right being zero and the left being somewhat higher. (2)

1. Follow that power wire back until you come to a supposed place where they should be the same, say, a switch. Measure both terminals of the switch. They should differ. You've now found the dirty, corroded, or faulty component.

2. Find out why the lamp socket shell isn't grounded ... loose screw, corroded, etc.

Again, parts is expensive parts. Don't start throwing parts at it until you prove to yourself that (a) this is the defective part and (b) it can't be cleaned or resurfaced.

Jim
 
Aren't those lights connected to the instrument dimming circuit? Has one (the right) maybe been reconnected to something else instead so it's bright all the time? Fool with the dimmer and see.

Or does it have the variable-iris lampholder that you turn to brighten or dim? Maybe that thing is seized and not closing.
 
weirdjim said:
Just don't start throwing parts at it to fix it. Take a voltmeter from the aircraft parts section of Harbor Freight. Measure the voltage to ground from both left and right bulbs AT THE BASE OF THE SOCKET where the bulb is inserted. They should differ, right being higher than left (1). If they are the same, then measure from the "ground" of the socket to a real airframe ground. They should differ, the right being zero and the left being somewhat higher. (2)
Click to expand...

Without the bulb in it the meter won't see a lower voltage. Not enough current in the meter's microammeter circuit to drop the voltage. I've been fooled that way, looking for supply problems without a load on the circuit. A breaker or a switch with a few ohms resistance won't drop the voltage enough without a load and the meter won't see anything, but the load still won't work.
 
Dan Thomas said:
Aren't those lights connected to the instrument dimming circuit? Has one (the right) maybe been reconnected to something else instead so it's bright all the time? Fool with the dimmer and see.

Or does it have the variable-iris lampholder that you turn to brighten or dim? Maybe that thing is seized and not closing.
Click to expand...
They are on the dimming circuit, and they all dim when I turn on the panel lights as they are supposed to. As in the left one becomes even dimmer than it already is.

The lenses are square so I don't believe there is any kind of adjustment to brightness at the bulb end of the system.

I'll try to follow Jim's advice and get my multimeter out to see if I can learn anything using it. Having three circuits that should be nearly identical should help me find which measurements are different on the offending circuit.
 
Dan Thomas said:
Without the bulb in it the meter won't see a lower voltage. Not enough current in the meter's microammeter circuit to drop the voltage. I've been fooled that way, looking for supply problems without a load on the circuit. A breaker or a switch with a few ohms resistance won't drop the voltage enough without a load and the meter won't see anything, but the load still won't work.
Click to expand...
I don't believe I said anything about taking the bulb out of the socket. I started by measuring the dim bulb's supply voltage.

JIm
 
GlennAB1 said:
Agree, the bulb contacts probably are cruddy.
Click to expand...
If that's the case, then I would expect to see equal voltage drops between each socket and ground and infer that there is a lot of resistance and thus voltage drop between the socket and the bulb. I haven't looked yet but I assume it's not hard to get to the V+ contact on the back of the socket. If this turns out to be the case, I assume my mechanic can order in a new socket and do a quick swap in the panel. Am I on the right track for this failure mode?
 
I'd remove the bulb and inspect the socket. Contacts should be shiny, if they are dark, or black, they may be cleaned up and be fine for years to come. Have done that many times.
 
GlennAB1 said:
I'd remove the bulb and inspect the socket. Contacts should be shiny, if they are dark, or black, they may be cleaned up and be fine for years to come. Have done that many times.
Click to expand...
Thanks. I'll bring my can of contact cleaner with. :)
 
GlennAB1 said:
That probably won't cut it. You'll need a tiny scraper of some sort.
Click to expand...
I'll bring the contact cleaner anyhow, but yeah...anything dropping the voltage enough to make it go as dim as it is will probably take a bit of effort to remove.
 
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