I've finished installing an all new wiring harness on my '34 and everything works but am having issues with, of all things, the dimmer switch.

The original worked sometimes and sometimes not so I went to the local O'Reilly's and picked up a switch they said fit from '29 -'54. But when I hooked it up (yes, correctly) it does not work - no lights at all. So I checked the switch and it shows continuity on both sides (alternately as you click the switch). So what gives? The box does not show voltage so could this be for a 12 volt, and if so, would it not work?

I can cross the wires and both filaments in each headlight work so I know the wiring and bulb sockets, etc. are in correct.

A 12 V would make the lights light.

A switch is a switch, volts are not a problem at that low of a voltage

It is possible that the switch is bad it can check good with a meter but fail when a load is put on it or what I mean is it will not carry the current of the lights but the current of the meter is a lot less. But it back in the car and measure the voltage on one side to GND and then the other side and see what you get.

That's what I thought but I cannot figure out why this switch won't work. Any more ideas?

It it works without the wires to lights being hooked, it should when the light wires are attached. Do you have the "hot" wire to the center terminal and then dim and bright wiring to bulb on the outside two terminals? If not then hook it up that way. All the dimmer switch does is switch between the two wires to the lights (does not matter which one goes on which outside terminal).

A dimmer switch is a very simple switch. Check that you have voltage to the center of the dimmer switch when the main headlight switch is on. Now check to see if the voltage changes from one side of the dimmer switch to the other.

I'm positive it is hooked up correctly - so maybe the switch is bad. I already have checked for voltage as you suggest. I can also jump from the battery terminal to either of the terminals to the lights and they will come on.

Do you have this diagram?

I agree with Andy, sounds like the switch will carry the low voltage for your meter but not the current required to light the lights. I would try another switch. I have seen many 110/220 v. fuses that would check OK with an ohm meter but not carry the full load needed.

I agree with you on the new switch not being any good. I'm taking it back tomorrow for a refund!

Yes, I have that diagram and a couple of others including the one that came with the wiring harness. Trust me, it is (and was) wired correctly! Realize I put the whole harness in with no problems and everything else works perfectly so I know how to wire this simple switch. The problem is either the switch or in the headlamp.

Anyway, I took the old switch apart, cleaned the contacts, put it back together, hooked it up, and now have it working on one side. In other words every other click I have lights.

Either I didn't get the contacts completely fixed or maybe it might be the bulbs. I will check them tomorrow to see if both filaments in each bulb are working.

Thanks for your replies!

Another thing to try is with the new switch in just but a jumper from the in put lead in the center to one of the wires on either side and make sure the light comes on than do the other side. Lights work switch is bad.

Well the problem(s) are solved! After taking the old switch apart and cleaning the contacts it now works properly.

The second problem, which I didn't consider until last night, were the bulbs since they were new, looked exact, and never used. But I dug around and found some old bulbs in a box, installed them and I now have both headlights with high and low beam!

The old bulbs were made in the U.S.A. Guess where the others were made.

The new switch that did not work went back to O'Reilly's for a refund.

Andy, your suggestion is appreciated and I had already used that method several times in trying to pin down the problem.

Thanks for all your replies. I learned something, maybe someone else reading these posts might also.

Having spent a career in plant maintenance and operation, I can tell you that in the realm of machinery and electrical equipment, few problems result in more wasted time and hair pulling than defective new parts. When troubleshooting, after replacing a suspected part with a new part, and the problem persists, you assume that the problem cannot be with the part you just replaced, as it is new, so you continue chasing your tail trying to find the problem elsewhere. It only takes one or two of these experiences to learn to consider the possibility that a new part may be defective. Especially those parts made in a certain Asian country.

Mark Yeamans
VCCA #35724