The Stovebolt Site Forums The Shop Area The Electrical Bay light switch

In January I ordered and received a new headlight switch for my 6V 1950 3100. It was the original design switch from Classic parts.
This last month (May) I finally got the old truck on the road and other than a few minor issues it has been great so far the few times I have driven it. Yesterday however, I noticed the right front Park light was not coming on and the blinker was dim (I always do a walk around before driving it until I am more comfortable with my work). Later in the evening when trouble shooting, I noticed the dash lights no longer worked so I turned the knob to see if they were just turned down too low and suddenly smoke started coming from under the dash. I shut everything down and disconnected the battery tip today when I had more time to check. I crawled under the dash today and found nothing melted, fried, blackened or any sign of fire. I reconnected the battery and looked again. I finally found that when I pull the switch knob to the first (park light) position the switch started glowing then smoking where the ceramic rheostat piece is. My question is, is it likely that the switch went bad? or is there something elsewhere bad that is just showing up in the switch because that may be the weakest link? Everything is new between the switch and the lights. I see know signs anywhere else of a problem.

Thanks

A short in the dash lights or a bad resistor on the switch. The resistor on the switch is pretty tough, so you might be OK. But you have to find the short.

This is a dangerous situation. Keep battery disconnected. Take switch out on bench, Test it's operation by continuity testing. Then be very sure you wired it correctly. Check each wire under dash for continuity to ground (a short as Steve said).
If all that is good you could hook up a 6V bulb to the rheostat/resistor/dash dimmer and to the park circuit using a 6V battery charger as a power supply (with inline fuse) to see if you can repeat the glow/smoke, outside the truck, on the bench, with this bulb as the "load". If you can not repeat the failure, then concentrate on wiring. Something somewhere is mis-wired or touching hot or ground when it should not. You can test the switch while hanging down on the wires, no need to install in dash where you can't see. You can also install the old switch to see if it does the same. While old or new switch is hanging down and wired up where you can observe/test, it may need a temp ground wire from it's metal bracket to chassis ground. It is possible the switch is bad but not likely.
Where exactly is it glowing? What is glowing? the windings on the rheostat? Sometimes when a switch gets mounted under the dash, the way you have the connections or wire routed lets a contact or unprotected terminal touch a place on the dash or a bracket under there. Think about anything else you have tinkered with before this test drive. Sounds like if everything is new, you rewired. Is this the first test after rewire/new switch? Hopefully the new wiring harness contained a new modern fuse panel.

Very dangerous. While you have the switch out, you can see if anything else is shorted, by being in a darkened place and unhook one battery cable, then get your eyes down close and watch for a tiny spark by barely touching the cable to the battery post. If you get a spark, then you got a short.
Of course this will not tell you about the lights wiring, unless you have power to them.
Good luck and be careful!

This was not the first drive after the new switch. I am guessing I must have bumped something when playing with the Gas gauge that just isn't obvious to me right now. I have the battery disconnected and will pull the switch out for some more trouble shooting this weekend. Thanks for the input. I will be sure to let you know what I find.

Did a thorough check under the dash, all the wiring was connected where it should, nothing touching where it shouldn't. I pulled the switch and checked it and it checked out ok (thank goodness, hate to buy new parts to replace new parts). So from there I went to the known bad spot, my right front park light. wires checked out ok so I pulled the bulb and it looked fine. I did notice however that the socket seemed to be pretty loose. I did the Airforce check of comparing it to the known good light which was tight. After getting to the screw in the back (not easy with the grill installed) I tightened it and put everything back together. Hooked it all up, crossed my fingers and pulled the switch on. Dash lights and parking lights came on as they should and no glow or smoke from the switch. I did it with the key on and the key off just in case there was something else involved. So far all seems to work again though I am skeptical of my work since this is the first and only vehicle I have really worked on more than changing the oil.

Take away from this for me is always do a walk around and check the truck out before you take it out. As a pilot I do that with the helicopters i fly and t makes sense to do it for this old truck. It vibrates a lot more than the modern cars and who knows what or when these parts, old or new, are going to fail from the stress. Check things out, and if you find something not working the way it should, find out why and fix it. Had my test drive the other day required the use of those lights I could have been in a hurt away from home with a fire under the dash every time I pull the switch all because I assumed I just had a build burnt out or something.

Thanks again for everyones advice and input, I'll let you know if anything more comes of this.

Roger all that. Think about installing fuses and/or fusible links in various places. Peace of mind/safety.

In-line fuse is cheap insurance. Hide them if you want. Use them to save the wire and your self

In general, does anyone have a chart of sorts that states what amp fuse for what circuit???

Jim, you need to make a list from accessory instructions .... aside from the small fuse on the light sw for the instr and tail lites [AD's have that?], which is 3a, this list works for TF years and likely will be the same for other series for the same items:
backup lites - 9a
heater fan - 9a
fog lites - 14a
park brake alarm - 9a
radio - 7.5a
spot lite - 9a
under hood lite - 9a
OD - 9a

Bill