Wiring problem

[Russell Reay]

Until recently I have been running the car with only the ignition circuit ---in and out of the garage. I just clipped the new Bratton's harness to the frame, attached the light switch to the end of the steering column, and installed the safety fuse. Attached wires to brake light switch, but otherwise all wire ends were unattached and not touching anything to create a short. Turned on the kill switch, and immediately blew the fuse. Double checked to see there was no accidental short, and concluded the problem is an internal short in the BL switch. With a meter there is no continuity between the switch attachment screws. Removing the wires from the switch and connecting them together there is no juice thru the fuse. All this with the nest of turn signal wires disconnected. Double checked the terminal box and solenoid wiring, and both are correct. I haven't removed the light switch from the steering column, but don't see how that could be of influence. Any thoughts?

 

[nkaminar]

It sounds like you are right that there is an internal short in the brake light switch. I have never taken one apart. Is there a way to disassemble the switch and try and fix what is wrong internally?

 

[JayJay]

Russell - There are brake light switches and there are brake light switches. Many of the cheap replacement units do not have bushings on the shaft, and they wear. You can take them apart (at least the later frame-mounted ones I’m familiar with) by carefully prying the tabs up and removing the insulated base, exposing the guts. If you have a no-bushing type I’d get a new one and throw the old one away. The vendors seem to have the crappy repops in stock but the good ones (quite expensive!) are out of stock. You might call Steve Becker at Burt’s to see if he has a good used one. I’ve had success opening the switches up, cleaning the shafts and contacts, and then reassembling.

BTW, continuity between the brake wire attachment screws comes when the switch is activated - the switch is a normally closed type that opens when the lever is pushed (brake pedal up) and closes when the lever relaxes (brake pedal down). On the bench the switch should have continuity between the two terminals that disappears when you push on the rod. If you short the two wires you should have current through the wires, to the brake light bulb and then to ground. When not jumped, one wire should be hot vs. frame ground and one should be ground through the bulb. So no/bad bulb equals no current flow. There should be no continuity from either switch terminal to ground, the terminals are insulated. If you get continuity from either terminal to frame ground then there is your short.

 

[jrelliott]

JaJay is correct about some of the stop light switches being being poorly made. On the switch I had the rod would slip inside the case and short out. Corrected it by soldering in brass tubes at each end of the case so the rod could not slip out. Have not had any problems since rebuilding about 2009.

 

[rich40701]

I found a NOS made in USA stop light switch on eBay and has performed flawlessly. Just like when Paul Shinn wired up Gandalf the Green and the electronic flasher blew after a few seconds so did mine. Once again I found a NOS made in USA 6 volt flasher and haven't had any more issues.