Headlight problems

[o2bnkc]

The other night I was coming home (1940 Deluxe, 6 volt, positive ground) and the headlights started flickering off and on. The first thing I thought of was a partially broken wire somewhere. I didn't find a broken wire anywhere, but when I pulled out the switch on the dash and turned it on, the headlight wire became hot to the touch. I've got 6.37 volts coming out of the switch to the headlight wire so I assume the switch is good. Do I have a bare spot somewhere grounding to the car? Electrical is not my strong suite. Thanks.

[51 MERC-CT]

Can be something as simple as dirty bad battery post connections.
Everything else you have to trace.

[o2bnkc]

Now the taillight wire is getting hot. It was smoking the connector by the firewall in the engine compartment When I disconnect it, the headlight wire cools off. With just the parking lights on, the taillights are very bright. With the headlights on, they are pretty dim.

[TJ]

Follow the light wires from the switch all the way to the front and back. Sounds like you have a bare wire touching some metal. If you have an old wire harness it may be time for a new one. '40 has a circuit breaker did you check it to see if it was getting hot?

[o2bnkc]

The current wiring harness was installed in 2012. It seems that both the headlight and taillight wires are overheating when the switch is pulled out. I've traced all the parts of each wire I can see. Where is the circuit breaker?

[51 MERC-CT]

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You can check the lines using the schematic as a reference.
This shows the location of the circuit breaker.

[TJ]

Originally Posted by o2bnkc

The current wiring harness was installed in 2012. It seems that both the headlight and taillight wires are overheating when the switch is pulled out. I've traced all the parts of each wire I can see. Where is the circuit breaker?

The circuit breaker is on the inside of the firewall just above the steering column. Also check your dimmer switch as the problem could be there.

[19Fordy]

Be sure to check all the slip in wire connectors that join the wires together

[corvette8n]

Also make sure you have good grounds everywhere, wire brush, file whatever you need to do to get clean, bright, tight grounds.

[51 MERC-CT]

And if you clean all the connections, I have had good luck lightly coating the connections with dielectric grease before reassembly to help keep future corrosion from forming.

[4dFord/SC]

Originally Posted by TJ

The circuit breaker is on the inside of the firewall just above the steering column.

Flashing headlights is the 1940 circuit breaker's way of telling you there is a short somewhere.

[o2bnkc]

Thanks for all the suggestions, guys. I don't see anything obvious yet. My dimmer switch is not even hooked into the wiring and I don't see any bare wires yet. Could the light switch itself, be bad?

[V8COOPMAN]

Originally Posted by o2bnkc

My dimmer switch is not even hooked into the wiring.

IF your dimmer is not even hooked into the headlight circuit (WHY?), how are you dimming headlights? This is obviously not normal, and indicates that someone has screwed with the system. Any other notable anomalies? DD

[o2bnkc]

LOL! I thought you meant the dimmer control on the dashboard lights!! So the foot switch can cause problems?

[40cpe]

Do you know that a 6V harness was used when it was rewired?

[o2bnkc]

I assume it was. The wire cloth coverings match the same color code as the original wiring according to my shop and owners manual. Red/yellow tracers for the headlights and a black wire for the taillights. I can't find a circuit breaker, though. I hooked up the ignition resister when I first got the car, but isn't the circuit breaker supposed to be up there by it? Can the dash switch be bad? That's the only place where the headlight and taillight wires meet up, and they both get hot.

[ford38v8]

The original circuit breaker does not resemble a modern unit, but rather, appears as a simple small black box, mounted on the same rectangular fiberboard as the ignition resistor. You said you hooked up the resistor, so I’m wondering if perhaps the resistor is routed incorrectly to the lighting circuit via the circuit breaker?

[V8COOPMAN]

Originally Posted by o2bnkc

I assume it was. The wire cloth coverings match the same color code as the original wiring according to my shop and owners manual. Red/yellow tracers for the headlights and a black wire for the taillights. I can't find a circuit breaker, though. I hooked up the ignition resister when I first got the car, but isn't the circuit breaker supposed to be up there by it? Can the dash switch be bad? That's the only place where the headlight and taillight wires meet up, and they both get hot.

They should be mounted on the same board, similar to this. DD

[drolston]

Originally Posted by 19Fordy

Be sure to check all the slip in wire connectors that join the wires together

Especially the ones on the frame rail just behind the radiator, on the left/driver side. That bunch is more exposed to getting jostled loose, and to corrosion.

If the dimmer switch is not connected, it may be that someone wired it so that both the high and low headlight beams come on at the same time. That would double the normal current load through the switch, wiring and circuit breaker, probably causing the circuit breaker to cycle and wires to get hot.

[V8COOPMAN]

Originally Posted by drolston

If the dimmer switch is not connected, it may be that someone wired it so that both the high and low headlight beams come on at the same time.

He finally explained in post #14 that he was referring to the DASHBOARD LIGHTING dimmer (rheostat). DD

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