Gear Down Light - PA24

[William Hughes]

The gear down light probably has 30 feet of wire and at least three switch contacts between it and the battery. When that resistance slowly goes up (age and wear) it creates a voltage drop and reduces the current through the circuit and the lamp. Incandescent lamps are touchy at low currents since the light depends on heating the filament and cold resistance is less than hot resistance.

The nav lights put a resistor into the ground side of circuit. Eventually the resistance will rise so that the gear up lamp will work (one switch short wires) but the gear down won't (three switches long wires).

A new lamp, new switch, or new resistor may make enough of a change that it might work. Resistors can have quite a wide variation in values and temperature can vary it as well. And a small incandescent is that touchy if the voltage is marginal. 12 volts will be brilliant, 6 volts might be bright, 4 volts is dim, 3.5 volts might be too dim too see.

The upstream voltage drop can only really be measured with the circuit hot. If the power to the light is well below 12 volts then there is a problem in the upstream circuit.

This exact thing is happening on my 250 and I'll be doing that comanche gear kit for certain. Plus checking the three gear switches.

[Zach Grant L1011jock]

You are absolutely correct on all counts above. The only thing I can add is that the Comanche gear wiring kit comes with all new switches so save your time skulking out the existing switches and just replace with the kit!

Zach

[Kristin Winter]

Any Comanche that has original wiring for the down limit switches on the three landing gear, should install Matt's kit. I haven't seen one original installation that would really pass an honest annual inspection.

[William Hughes]

Got down on the grass and had a good look with a light. Very sobering thing. New harness is on the way.

[Duane Bolin]

I have LED installed in the green and amber gear lights and they work well with the nav lights on. Not to concerened with the inability to dim the amber light as I don't do much night flying. Purchased from Aircraft Spruce, LED Midget Flanged Bi-Polar Lamp T1-3/4 (5-28 volts), it has a very long bulb life. This bulb replaces many flanged mini bulbs including the 330 bulb that was installed on my aircraft.