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Chasing down the cause of brake light failure in my '73 KaryVan and have almost narrowed to the hazard light switch. I have turn signals (after replacing the broken cam), and power to all the switches. Bulbs are new and come on brightly with turn signals.
I can get runners to come on. Brake switch tests fine, both power and continuity. Continuity in all the steering column wires test good. New flasher relays.
But i have no brake lights and the hazards only come on in the front (turn signals come on front and back). Could a bad hazard switch still work in front? And is there a way to pop that little box open? It's riveted shut and the plastic looks like it would break apart if I tried.
I have a replacement column harness ready to order but it looks alot cheaper than stock and I'd have to cut the different connector to make it work. Hoping someone has ran across this.
Since you have replaced the canceling cam I would look closely at the inner or right most (closest to the steering shaft) "wire whiskers" of the cam. When the cam switch is in the neutral position these "whiskers" should be touching the contacts responsible for the rear lamps. Specifically the filaments used for Turn/Hazard signals and Brakes. Parking lamps are a different filament and are not routed through the turn signal switch.
You may need to bend and lightly tweak the whiskers or try applying lite downward pressure to the cam using your finger.
You could even use a test light with one end connect to a good ground. If you touch the probe end to the center where the wire connects. The test light should turn on when you press the brake pedal (with the hazard switch off) and the test light should blink if you turn the hazards on.
Other than that make sure the rear lamp housings have a good body ground.
This is knowledge I've learn from working on the trucks and not the vans. So I'm not sure how much will crossover.
Below are more details.
Hope you find this useful.
Originally Posted by dodgem880
There are two flasher cans. One for turn signals and one for hazards.
When you turn on the hazard switch there are three things that happen:
Power from the hazard flasher gets jumped to the Front Left and Front Right turn signal lamps
The Rear Left and Rear Right signal lamps connection with the brake stop switch is severed.
Power from the hazard flasher gets jumped to the Rear Left and Rear Right signal lamps.
As you can see, the rear signals are a little more tricky because they double as a brake lamp. Even when making a normal left or right signal, the "cancelling cam" first breaks connection with the brake switch before apply power from the flasher. Also, Both the brake switch and hazard switch rely on the "cancelling cam" and it resting in the center position for powering the rear signal/brake lamps.
One important thing to note is parking lamps are done by a separate filament and are not handled by the turn signal or hazard switch.
I recall in the 70s while working at the Dodge dealer we had unexplainable rear light problems like yours. It was a long time ago but the fix was in the turn signal harness. Without pulling the wheel and changing it, first disconnect the harness where it connects at the base of the steering wheel by your knee. Place the new harness in with it hanging and see if that's your cure. I've seen this many times I just don't recall what lights didn't work properly.
I owe you a steak!
I took the cam back off and sure enough one tine was angled down too far to make contact. I took emory cloth to all the connecting points, adjusted the tines out and put back together. Still not getting one side rear hazard but maybe after another tweak it will connect.
The important thing is that I have brake lights now. Thanks a million for the tip.
I remember an old-time mechanic at the Dodge dealer with about 30 years experience telling me when you have no rear lights after checking the fuse, plug in a new harness at the column and it usually fixes the problem. That old guy rest his soul is still fixing cars by passing on his knowledge.
05-10-2023, 03:03 PM
