1934 Fordor headlight problem

Feathercraft56

Feathercraft56

Member
I have a stock 1934 Fordor and when I apply the brake, the headlights turn off and when I disengage the brake they turn back on.
I replaced the factory headlight/horn/tail light harness and all factory female connectors as well. At the exact same time when the brake light switch engages the tail lights the headlights turn off and automatically come back on when brake light switch is disengaged.
Any help would be appreciated very much.
David
 
You didn't say if this problem was happening before you replaced the harness. Sounds like its miswired to me. Here's a wiring diagram >
Flathead_Electrical_wiring1934.jpg

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If there is a short circuit in the stop light or its wiring or switch that will cause a lot of current to be drawn which would rob the other lights of power. Having said that the single under dash fuse should blow if the wiring is connected as it should be through the fuse. The only way to fix this fault is to follow all the wiring along very carefully and find the short circuit. Look also inside the stop light bulb sockets for anything touching to ground. Make sure there is no wiring being jammed by the brake pedal as it is pushed down. Regards, Kevin.
 
Have you made sure the brake pedal is not touching any of wiring harnesses when depressed?

If you find the problem in the light switch be aware Ford did not draw the electrical wiring diagram as shown above in post #2 correctly. They did not show the key way on the OD nor indicate what side of the light switch wire terminal plate they drew or any of the OFF positions.
 
Hello all. Still having same problem. Checked all wiring and connections to no avail. I noticed if i run the car a high rpm the problem goes away completely and when you ideal down and hit the brakes the headlights start to flicker and then go out until you stop braking. One thing if forgot to mention is i am using LED headlight bulbs and there for 6volt and positive ground. They work fantastic like a new car does. Theses bulb require vary few amps (less than stnd bulbs.
Could the generator be the culprit??? There's nothing else to the electrical system i can think of.
 
I don't see how it could be the generator. Keep looking and keep us informed on what you find.

Merry Christmas.
 
Terry said:
Have you made sure the brake pedal is not touching any of wiring harnesses when depressed?

If you find the problem in the light switch be aware Ford did not draw the electrical wiring diagram as shown above in post #2 correctly. They did not show the key way on the OD nor indicate what side of the light switch wire terminal plate they drew or any of the OFF positions.
Click to expand...

The GREEN image BELOW shows a better detail of how that switch (phenolic) is wired. The second pic shows the brass-looking ring (conductor), which is what is rotated-around as you twist that switch into different positions.

Three OFF positions are when the three divots in the brass ring line-up with the three recesses in the phenolic, where the three points of the dotted triangle meet on the GREEN drawing. In NORMAL operation, the two finger protrusions on your twisting light switch surrounding the horn button should line-up straight up and down at 12 & 6 o'clock positions when lights are OFF. DD


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I'm on the same page as Terry, OH. Given that these old Ford use a chassis ground for just about everything, it is super important to have good clean grounds for all circuits. I'd check/clean the ground from the battery to the chassis (can't remember where it hooks up on a stock 34???). Also, make sure you have good grounds to all your lights. It may be that when you apply the brakes, the movement in the chassis is temporarily causing the chassis ground circuit to break. Also, you might want to (at least temporarily) add a heavy ground wire/strap from where the battery ground connects to another cleaned part of the chassis - to help you troubleshoot it.

Also, see if when you run a temporary ground wire (just a chunk of wire for testing) from the headlight/taillight buckets to the ground side of the battery - if things work. If so, then you know where to start looking.
 
Bad ground or if your still using the circuit beaker on the firewall you may be tripping it with load when the brake lights come on. Had this happen when doing lighting upgrades. Tim
 
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