VCCA Home Forums TECHNICAL - 1945 AND NEWER 1946-1948 1946 Chevy Truck Lighting short

I have an restored 1946 Chevy truck with the 6 volt electric system. There is a short in the lighting system. As soon as I turn on the lights the fuse blows. I have inspected all the wiring and can not find anywhere that the wire is shorting out on metal. Could the problem be in the light switch. I notice there is some kind of electrical component on the inside of the light switch.
Does anyone have an idea how I can fix this?

The easiest way is with a multimeter however if you disconnect the wire from the switch TO the lights you can determine if the wiring to the lights is shorted or whether its between the switch and the power source. From what you have described I agree the switch is probably bad and should be replaced or repaired if possible. If you don't have a multimeter they are very inexpensive and easy to use. Harbor Freight sometimes even has them free with special promotions.

About 7 years ago I was having problems with my lights blowing fuses. The problem was in the dimmer switch (rheostat). When I bipassed it I eliminated my problem. In my case the lights would stay on until the rheostat got hot. When the wire expanded enough it would cause the wire to short (break open at a corroded spot) blowing the fuse. I changed my light switch wiring so the dash lights would come on with the lights at their maximum brightness. At age 66 I wanted the brightest dash lights so I could easily see all the gauges.

It is not uncommon for the spring to corrode over time, 60 plus years.


The first picture shows a typical rheostat. you see a circular spring with a small metal finger riding on it. The position of the movable finger is what is allowing your lights to be dimmed at various degrees.


http://i1321.photobucket.com/albums/u560/41chevymike/IMG_0386_zps1999c3f6.jpg


This picture shows the finger riding on a post. The finger could end up riding on either of the two posts. One post is for turning the dash lights all the way off the other for turning them all the way on.



http://i1321.photobucket.com/albums/u560/41chevymike/IMG_0388_zpsb2ac54ff.jpg

The easiest repair is to buy a new switch. They are available at Chevs of the 40's or The Filling Station, both are major Chevy part dealers and they both have web sites with their catalog of parts. If you are real adventuresome you could take a rheostat off another switch and exchange it for yours. I would only recommended this if you can not find an original looking replacement.

Good luck, Mike

Actually, this is not the way it works. The rheostat is used only in the control of the brightness of the dash lights. If a wire is broken, it stops the flow of current and does not cause a short.

To isolate the short the first thing is to determine what circuit is the guilty party. Start with the light switch and pull to the first detente, this is the parking and dash light position. If it blows the fuse, remove the wire from the switch and check if the short is removed. If it does NOT blow the fuse, go to the second detente. If it blows the fuse there the short is in the headlight circuit. Remove one of the wires from the dimmer switch. No short, the problem is in that line. If not, remove the second wire and if that removes the short it is on that line. Now move up to the headlight blocks located under the hood. One on each side of the engine compartment. Start with either one and remove one wire at a time. If you still have the short, it is in one of the lines to the headlight bulb. Check each line as before. If still shorted remove each line one at a time and check.

Trying to find out why the smoke is getting out of a line is a real challenge, however a purposeful plan will help in rutting it out.