The Stovebolt Site Forums The Shop Area The Electrical Bay Brake light mystery

The brake lights on my 1950 3600 refuse to work. The tail lights also did not work and crawling under the truck, I found two wire splices, crimp on butt connectors and the tail light wire was easily pulled out so I figured that was the problem with both. The wiring harness is original cloth covered stuff and is a bit on the decrepit side but the wire to the aft of the butt splices was common lamp cord. I put new 14g wire in for both and get 5v at the tail light wire but 0v for the brake with the pedal depressed. I checked the brake light switch which is a new replacement and there is 6v on both terminals with the pedal depressed. The wire that I think should be running back to the brake lights runs through the firewall by the steering column and I am guessing up to the signal stat add on directional set up which I have never used. The whole unit is bundled up and tucked under the dash and has been for the last 40 years that I have owned the truck as I have relied on hand signals for the most part. I am thinking that the problem may in the signal stat wiring somehow. Anybody have any ideas to help me figure this out?

I once had an issue with tail lights and bad wiring. I pulled it out and replaced it with an extension cord that had the ends cut off. I'm sure the next owner(s) scratched their heads on that one.

There are a couple of fairly recent threads pertaining to installing add on turn signals that might help you out.

Truck needs a new wire harness all around. Pretty easy to do.

If you're not going to use the turn signal switch, find a fused power source and some new wire. Go fused source to brake light switch, then switch to brake lights. Problem solved for another 70 years. Why add something inline that you'll never use?

The rear tail lights and the front parking lights wiring, are separate from the turn signal switch.
They both are fed from the headlight switch.
On the headlight switch there is a terminal for the rear tail lights and a terminal for the front parking lights.

The brake light switch is fed voltage from a terminal on the headlight switch.
The brake light switch is connected to the turn signal switch.

The turn signal switch, switches between two sources:
1. The flasher module
2. The Brake light switch

What is the model of your signal stat add on directional set up?
Do you want to make your signal stat add on directional set up function?
Are your rear tail lights and the front parking lights working?

Note: Attached photo wire colors apply to 1954-55 1st signal switch color scheme.

xfiles

Thanks for all the replies!
Replacing the harness has been a thought but the under the dash part is not something I look forward to. I reinforce myself by saying the wire in it is still original. Definitely past its prime though.
I have a wiring schematic from the manual (no directionals) and wire goes from the dash switch, fuse box, brake light switch and straight to the tail light.

Have you checked the ground? My stop/tail light housing was rusted between the metal housing and the bulb holders. Run a wire from a known good ground and re-test for voltage. If you have voltage, you know you have a ground problem.

My truck has a non original rear bumper that was welded on to the frame. I am using the bare spot on the bumper brackets (where I had removed the old tail ight brackets by grinding) as my ground. The ground strap from the battery to the frame was also cleaned so I am reasonably sure I am getting a good ground. And am using new lights.

If your getting voltage thru the stop light switch and you ran a new wire to the back where the stop light is, something from that switch to the battery ground is not allowing it to complete the circuit.

I would still run a ground wire from the battery back to the stop light location and check for voltage from your new wire previously installed and the ground wire you just hooked up. If still do not have voltage, re-check the terminal at the switch and then check continuity of that new wire you installed.

Question: "I am using the bare spot on the bumper brackets (where I had removed the old tail ight brackets by grinding) as my ground." What exactly is "my ground"?

The test described by Phil is to take a voltage tester (meter or light) ant touch one probe to an absolutely sure ground (which could even be a wire all the way from battery negative post) to the contact inside the bulb socket after you take the bulb out. Then we can go from there, one step at a time. Nothing is for sure until you start testing as we describe. As we would do with our own truck. Report your findings.

Many of us do not use the "25 things it could be" approach. Most of the time we use testing.
Check for voltage with a ice pick tester at the bulb contact, pedal depressed, using a dedicated good known ground. Check both tail lights. Check both bulbs, both filaments, by taking bulbs out and checking them at the battery or any 6V battery. Voltage is the easy part of the circuit to test. Ground is much harder. That's next.

Ok folks, I may very well be the last human in the U.S. that thinks 6 volt is a wonderful thing. This is the best of that period of simple automotive electronics. Why; carries much more amperage (that's why the bigger wiring and cables), the big non-secret is two very wire brushed ground straps. Polish them every three months depending on humidity, also the frame or what ever the BRAIDED cable is attached to AND be sure to attach a star washer. This combination also needs to be put into a baking soda solution every once in a while. I have never had any problems with six volt systems, I still race vintage sports cars and all but two are 6 volt. It's just a matter of choice and maintenance. Also never let anyone with a 12 volt system beg you to give them a jump, it will burn EVERYTHING in their auto's to a crisp. OOPS. Doc
.

Will all respect to you. With all respect to maintaining an original 6V system. There is another side to the story which does not include keeping the 6V. Just like we abandoned using outhouses and we prefer indoor plumbing, power steering and brakes, overdrive, Pertronix, turn signals..............
The 12V system has lasted way longer as a good system. Here are a few thoughts. they won't change your mind, but are necessary for anyone thinking of changing and not quite that nostalgic or as pure as others.

For those wondering why convert to 12V as GM did in 1955:
1. No big huge cables required
2. You can buy a 12V battery anywhere.
3. Faster starting, especially in cold weather.
4. You can add accessories, winch, electric wipers, radios, extra lights......
5. You can by bulbs anywhere
6. You can't get a jump start from someone without burning out bulbs and gauges.
7. Automotive is built around 12V systems
8. Testing is built around 12V
9. Aftermarket is built around 12V
10. You can buy a 12V alternator anywhere and cheap......and has way less wiring. You can't buy a generator or Voltage regulator anywhere and cheap.
11. Brighter headlights and tail lights, no need for relays
12. You can charge your cell phone
13. 6V takes twice the current/amps to get the same watts. If you have 50W hi beam headlights, they will draw twice as much current as on a 12V system. I.E. 100W (both headlights) is 100W/6V=16.7 Amps vs 100W/12V= 8.33 Amps. This is why 6V wires/cables have to be so big.
You can run out of amps on 6V. (and have dimming, etc). Then you start band-aiding with relays, voltage regulator tricks or living with it.
14. May take a special harness to rewire a 6V truck.
15. It's so easy and inexpensive.
16. There is no reason not to convert except to prove something...........I don't know what.

For the purest, to prove it is original.