I'll try not to make this too long but will give as much info as possible. This truck had a new harness put in it 20 years ago when we restored it, but has actually never run at night for any length of time. When I turn the headlights on, the headlight switch and power wiring to the swith and then from the switch to the dimmer switch gets hot enough that it can burn you(don't ask how I know that) If left on long enough it will eventually burn the 30 amp fuse that is on the switch. A couple of details then I will tell you what I have done to troubleshoot so far. This truck is original with the 6 volt system still intact. When we replaced the battery recently to get it running my grandfather suggested an 8 volt battery. That's the way he ran his back in his day. We installed an 8v battery. To date I have done the following. I checked the battery voltage and it was 8.7 volts. I put my meter that is rated for 20 amps in series between the switch and the power wire to the dimmer switch and read 17 amps when the headlights were on. I switched from high beam to low beam during this time and didn't see a significant difference. During this testing the wires where heating up quickly. I measured 120F within a minute of turning them on but never saw the amps go above 17. I disconnected one of the headlights and checked the other by itself and read a little over 8 amps. I reversed this and checked the other light and it was also 8 amps. I also checked the tail lights by themselves and it was only a couple of amps and then the dash lights which pulled less than 1 amp. I have several ideas but would appreciate your opinions. I did a couple of calculations and could it be that the 8 volt battery is causing me the problems? The amperage readings I am seeing with 8.7 volts instead of 6 increases the wattage quite a bit. Grandpa said he did it all of the time but I'm wondering if the 8 volt in combination with the possibility that this harness might have smaller wires could be the trouble?

What am I missing and where should I go from here?? I have replaced the dimmer switch because I initially thought it might be the problem. I purchased a new three position switch today to replace the switch that got a little hot. I want to do more troubleshooting before I try again.

Thanks for the help!

 

Not real familiar with the 6V system, I had a problem similar to that with my headlights but with 12V. The light switch got real hot after the light were on for a while. I also had problems with the high beams making my headlights dim. I basically traced the wiring from the power, to the fuse, to the headlights, to dimmer switch. I found a few connections were loose. I put new clips on the wires and replaced a few that were questionable. What ever I did worked. Headlights are fine. Sounds like a loose connection somewhere.

 

Six volt systems do require larger wire than 12 volt and the 8V battery is probably adding to the problem some. So, if you think the wiring is smaller than the original size, that could be a factor. You could try running the headlights through a relay. Just use the headlight switch to trip the relay and wire the relay to the headlights. That might solve the problem. However, if leaving the lights on causes a 30A fuse to blow, then you may have other problems too. make sure all connections are tight and you have good grounds.

Vern

 

Boy, it sounds like you have short in the wiring somewhere to me. Make sure the wires aren't chafed where they go thru into headlight buckets. Been there done that. Mine would only get hot sometimes, hit a bump and everything was OK. Also make sure you have a GOOD quality Headlight switch.

 

A short would blow the headlight fuse immediately. It has to be a bad connection or not heavy enough wire...even a bad switch.

Vern

 

Headlights should be wired thru a relay, no switch is going to handle that much current for very long.

 

My 55 is 6V but using the best interstate 6V battery they have. Figure if it was good enough in 55 should be for now too. A guy in my truck club runs an 8V bat in his 50 Ford car with no problems.

Fred K.

 

I did some troubleshooting without the switch involved. Even without the switch when I connect the hot wire to the power wire going to the dimmer switch, the wire gets hot. The dimmer switch is new but the terminals on it get warm also. Does anyone know how many amps the two headlights should pull??

Thanks for the feedback.

 

What size is your power wire going to the dimmer switch? It should be at least 12 gauge for 12 volt systems and possibly larger for six volt (not sure). If you aren't sure what size it is or if you think it's too small, try using a larger diameter jumper wire and see if it still gets hot. I do not know how many amps 6V headlights pull, but I would think less than 30 since that's the size fuse on the switch. Most modern 12v systems use a 30A fuse for the headlights...

Vern

 

A wire getting hot is just too thin for the circuit and/or a connection at one end may not be tight enough. Like Vern says, run a temporary heavier gauge wire with the ends tight and I'll bet it will cure your problem.
Norb