Landing light switch

[voorheesh]

I have a 1950 170A and it has the piano style electrical switches. There are 2 switches under the landing light placard and the right one is stuck in up position. I just realized that someone before me wired the the two lights into the remaining left switch and put a 30 amp fuse in. The wire gets hot if you leave the light on for any amount of time which is not right. Questions: There are two switches in the 170A for landing and taxi lights, right? Can you get replacement piano switch parts and if so from where? Are the piano switches attached to each other or are they single units? If you can't get replacements, has anyone ever repaired one? Thanks for any help.
Harlow Voorhees
Fresno

[blueldr]

The switches in the piano console are all standard SPDT switches. Those limited to a ST are restricted by a mechanical tab that can be removed to provide for DT operation. Some airplanes seem to have the landing and taxi lights wired on a single switch using a DT, others use two separate switches operating on ST.
At any rate, the two lights should not be on the same circuit simultaneously. Too much load for the wiring.

[KS170A]

The original wiring schematic for the 170 has two 14-gauge wires going to the lights (one for each light). Portion of that drawing attached. I'm installing a DPDT switch w/ a jumper and without the tab so I have one light illuminated in one position, and both illuminated in the other. Also changing the fuse to a circuit breaker.

[n2582d]

Take a look at the picture and discussion here as well as the IPC illustration below. Your piano key is "stuck" in the up position is because it is fastened with a screw (item #48)--there is no switch attached to that piano key. Both the landing light and the taxi light are controlled by one switch. Cessna only got around to having separate circuits for the landing and taxi lights on the late model C-170B's.

The AN3021-1 switch (item 34-40 in the parts manual) is available from Aircraft Spruce.

The original wiring schematic for the 170 has two 14-gauge wires going to the lights (one for each light).

That is true for the late model 170B's. The IPC for the C-170A on page 55 only shows one wire (item 30-74) going through the wing to both lights. The 170A wire chart doesn't say what gauge wire is used there but the early model 170B's use a 14 gauge wire to power both lights together. In looking at figure 11-2 of AC43.13-1B the wire should be at least 12 gauge--probably 10 gauge--to handle 200 watts (15.4 amps @ 13 volts running 16 ft.). 14 gauge wire is adequate for intermittent use--less than two minutes at a time. If you want to have the landing and the taxi light on individual circuits you will have to string two #14 gauge wires from the switch to the landing/taxi light. You might as well replace the old wire with new Tefzel wiring. I would try attaching two 20' lengths of wire to the existing wire at the lights and then pulling that old wire through the wing. There should be a connector on the existing wire at the wing root but I wouldn't put a new one on the replacement wire--one can do that whenever the wings are removed. You could install a DPDT switch as suggested for operating both lights in one position and just the taxi light in the other position or you could add another single pole switch and replace the screw (item 34-48) holding the adjacent piano key in position. The fuse holder originally held a 25 amp. fuse for the landing lights in your plane. If your "piano keys" are sagging you might want to replace the AN 931-4-7 grommets (which go around the switch lever) while you're replacing the switch. If you think you actually have a problem with the way your plane's wiring is set up I'd be glad to give you a hand fixing it. I'm off work for the next two weeks--come up to Mariposa and I'll help replace the switch and/or wire. If you're interested in modifying your system to have seperate control of the taxi and landing lights ask Joe Salazar, my PMI, if he wants a 337/field approval. I'm of the opinion that it is a minor alteration--just a logbook entry.

[voorheesh]

Thanks for the advice.