Stop lights still not working 40 coupe

[Terry,OH]

Repeat your power test at the stop light switch with both tail light bulbs removed. If there is power to one of the wires on the switch it would appear there is a short circuit at one of the tail lights between the black and green wires. drolston is correct the green wire to the circuit breaker may be broken or disconnected (open circuit) under the firewall cover for the wiring. If you remove the firewall cover do it with the battery disconnected.

[mike42]

Terry……

I had a similar problem this past summer with my ‘40 and got all the great advice as you have. Looked into each one and it came down to worn out wiring in the kidney cluster on the firewall engine compartment. Since I didn’t wish to tackle the complete rewire I elected to run a separate new 14 gauge wire from the stop light switch to the rear and connect to the rear lamps. I made a small jumper wire with alligator clips to see if I was getting power to the switch and I was, so I then ran the new wire bypassing the cluster on firewall. I then took a heat shrink tube and blocked off the old wire and tagged it as old wire. It’s probably not the proper way to do things, but it was Summer and I wanted to drive my car !! My car is still 6 Volt. Good luck !

Mike

[Fordyguy]

I did look at it again today but I still haven’t determined the issue. I can say that all the wires are color coded correctly. I have good ground at the tail lights also. I checked all of the wires in that housing on the firewall and they are all connected properly. The green wire is hot there and at circuit breaker but not the stop light switch so I guess maybe a short in between there and stop switch? I just find it odd that it has been working and all of a sudden, I have something not right by only switching out brake light switch. Head scratcher for sure.

[drolston]

To be clear on terminology: a "short" would mean a hot wire touching ground, which would open the breaker, blow a fuse, or fry the wire. It seems that you have an "open" circuit. Like a broken wire or bad connection at either end. If water gets under the insulation of those wires, the copper can corrode to the point that it goes open circuit. In the process of installing the brake light switch you may have disturbed the corroded wire inside the insulator enough for it to break the connection. If you see any light green on the metal at either end of the wire to the brake light switch, it is very suspicious.

To test this theory, get a wire that will reach from the battery hot side to the brake light switch. touch it to the wire that goes back to the break lights and see if they come on. If they do, run a replacement from the green wire coming from the breaker to the brake light switch. 14 gauge stranded copper should be adequate.

[Fordyguy]

I will try that tomorrow. This car hasn’t been wet in 25 years other than washing. Thanks for info.

[cas3]

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You can have a bad connection at the crimped on bullet connectors. The wire may be hot, but the bullet is not.

[Terry,OH]

At the firewall cover each wire into a bullet splice connector has two sides, you have to check both sides of the green wire. I think you will find one green wire is not pushed into the connector all the way. Use small needle nose pliers to grab the wire as close to the bullet termination and push it into the connector. If both of the wires are hot then the green wire to the stop light switch is open circuit. Usually find poor connections at terminations from the wire to the devices at either end.

[Fordyguy]

I’m just getting a chance to check it again. I ran a jumper wire straight from battery to stoplight switch to check. Brake light works but now my dash lights come on am I press the brakes. If I turn on headlight’s and press the brakes doesn’t seem to work. Only when headlights are off. Both filaments are still on when I turn on headlights. All of my wiring on the firewall look correct. The green is hot on both ends of connectors. As stated before, they have been working fine for years.

[glennpm]

Originally Posted by Fordyguy

I’m just getting a chance to check it again. I ran a jumper wire straight from battery to stoplight switch to check. Brake light works but now my dash lights come on am I press the brakes. If I turn on headlight’s and press the brakes doesn’t seem to work. Only when headlights are off. Both filaments are still on when I turn on headlights. All of my wiring on the firewall look correct. The green is hot on both ends of connectors. As stated before, they have been working fine for years.

Seems like you haven't traced green wire from the brake light switch back to the circuit breaker and you probably have a green wire abrasion to one of the headlight wires, feeding power to the green wire.

Do you have a VOM and know how to use it?

"How To Test a Wire for Continuity

Touch one of the multimeter (VOM) leads to a male prong and insert the other probe into the corresponding female receptacle. If you get a zero reading, the wire is unbroken.
After checking the other wire, cross-check by touching the probe to one of the male prongs and inserting the other probe into the opposite receptacle. You should get no continuity. If you do, it means something sliced through the insulation and the wires are touching each other.

You can also test a lamp wire by touching one probe to one of the male prongs on the cord, the other probe to the light socket, then turning the switch on and off. You should get continuity with the switch on, and no continuity with the switch off."

- The VOM will have an Ohm symbol, Ω. Switch to Ω to check resistance.
- Check the resistance from the brake switch back to the circuit breaker.
Write it down. Alligator clips are handy for this.

- Follow the green wire from the brake switch back to the first bullet connector.
- Unplug the connector and write down the resistance from the switch to the bullet
- Check the resistance from the female connector back to the circuit breaker and write the value down, etc.
- Check the green wire for abrasion especially where it crosses other wiring. You may find that the headlight wiring is contacting the green wire.

Please make a quick sketch, noting connectors.
Post this along with the Ω values for each segment.

Glenn

[rich b]

Originally Posted by Fordyguy

I’m just getting a chance to check it again. I ran a jumper wire straight from battery to stoplight switch to check. Brake light works but now my dash lights come on am I press the brakes. If I turn on headlight’s and press the brakes doesn’t seem to work. Only when headlights are off. Both filaments are still on when I turn on headlights. All of my wiring on the firewall look correct. The green is hot on both ends of connectors. As stated before, they have been working fine for years.

Seems to me the only way the power you jumped to the brake lights could be getting to the dash lights is back feeding to the dash lights thru the tail light wire; I would double check tail light body ground, bulb socket to tail light body connection, a bulb that is not grounding to the bulb socket, or even an internally shorted bulb.