36 new wire harness, no tail light or brake light

J

Jacks 36 Find

Junior Member
Hello and help please. I rewired my 36 standard with a complete wire harness from CW MOSS. it looks great and original. Everything works great except for the tail light and brake light. I reviewed many of the forum threads but didn’t find a similar situation. First I have continuity for the black tail light and green brake light from the switch back to the tail light. I’ve tested the tail light off of a battery and both filaments light up. When I turn on the parking lights they light but not the tail light. The low beams and high beams also work, but no tail light or brake. So I thought I might have a bad ground and clipped a jumper cable from the light housing to my bumper and then both work - once. When I try again I blow a fuse. Without the ground jumper no tail lights at all. With the jumper one time light then another fuse is blown. So I’m wondering if I’m trying negative ground fixes with a positive ground system? But without a jumper I get no tail light. Any suggestions or help would save what’s left of my sanity. Thanks Jack
 
JSeery
Member Emeritus



Join Date: Nov 2012
Location: Wichita KS
Posts: 16,132


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Re: 1936 electrical problem
The photos are of a Model A light switch I believe, but they are all very similar. As you can see from the wiring diagrams, the brake light wire is connected directly to the power in wire. That would be the first thing to check, if there is not power to the brake switch then there is not power to the light switch.
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Jack
Read this and see if it answers your questions.
Is your car still 6 volt? Are you wiring in turn signals? Do you have a VOM tester?
These details will help getting the solution for your problem.


Bruce
 
You didn't say if your 36 is pos or neg ground. But, for the lights to work, that shouldn't matter. My 36 is 12v neg ground and the rear lights work fine. terry
 
You may have a problem with the tail light bulb socket. Suggest you take the light apart and look things over. Are you using the 1158 light bulb? Are the slots in the bulb socket for even pin light bulb or the staggered pin bulb.

You may have two problems, one being no ground to the light, the second may be the light bulb or the bulb socket.
 
I’d remove the bulb and with a continuity meter check for continuity between the contacts in the socket to ground. There should not be any. There should be continuity between the socket housing and ground .
 
I had a similar problem recently, and found that the bulb socket shorted the wires when the bulb was inserted. The wires moved back and grounded on the opening of the bulb socket. With out a bulb installed there was no short.
 
Hello Bruce. Thanks for the reply. I’m new here and I think I’m having as much trouble navigating through the forum as I am my wire harness. ��. Just to confirm my car is 6v positive ground. I’m looking at your attachments but when I enlarge them they are fuzzy. I don’t know if you could or would PM if that’s possible. I rewired my original 1938 Ford and street rod 1940 and I didn’t have this much trouble. Maybe I’ve lost enough brain cells over 74 years where I’ve created a block. No matter I need to get the lights working. I had all the headlights and parking lights working. As I mentioned in my post there was no lights at the tail light, or brake light. I had continuity to the connection for the taillight & BL leads. But when connected, nothing. That’s why I tried the ground wire. It worked. Brake light and tail light, but only once then the next try it blew the fuse. That’s what is weird. If I had a bad connection it should have blown the fuse first time. (In my mind). I tried again with the same results. I probably buggered up the entire deal when I cleaned all mating surfaces on the tail light housing, chicken leg and support bracket. That would have worked with negative ground but not positive. I’ve ordered a new taillight assembly and will try again after it arrives. But if you could send me this images where I can blow them up I would appreciate it. Regards Jack
 
"I probably buggered up the entire deal when I cleaned all mating surfaces on the tail light housing, chicken leg and support bracket. That would have worked with negative ground but not positive."


Being negative or positive ground has nothing to do with it.
 
The tail light is a new assembly from CW Moss and I got the correct 6 volt bulb from them at the same time. The ground I think is the issue. But, I’m trying to work with positive ground but thinking in terms of negative ground. The wiring diagram that came with the harness show a ground at the tail light and I would think that bolting the taillight, chicken leg housing and support bracket to the frame would provide the positive ground. The headlights work that way so why not the taillight? One “simple” taillight has been my biggest challenge. ��
 
Jack,, I am thinking that you have contact alignment problems in the rear stop and tail sockets. The bulbs must match the sockets as in the pins on the sides of the bulbs are either offset or in line and must match the slots in the sides of the sockets. You could have either type. Also once the bulb is seated evenly into the socket then the tail and stop contacts on the bottom of the bulb must line up with the contacts in the bulb holder. These are available in TWO STYLES and you need to be correct here. As for the earthing, forget weather it is NEG or POS ground battery connection, it does not make any difference as long as the bulb sockets have a good ground to the chassis. Check the above out before getting involved up in any other parts of the wiring. Regards, Kevin.
 
Are you running regular bulbs or halogen? What size fuse 10 amp? Sounds like a ground issue except the blown fuse.
 
Jack
Remove both wires from the brake light switch and connect them together, brake light should be on. If so then get another switch.


Bruce
 
Do you have turn signals? A fault in the switch or wiring can affect the other light functions. I had that problem just yesterday where a loose connection there prevented a brake/turn light from working then a short and blown fuse.
 
Did that and connected manually and got light. When I had wire harness connected the brake light worked when stepping on the brake. But that only worked once..
 
The bulb matches the socket. Pins are offset and contacts on bulb bottom match up to contacts in light socket. Also, I’m using a 20 amp fuse.
 
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