brake light teaser
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New User
Joined: Dec 2003
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From: Washington
brake light teaser
My 74 flatbed has completely confounded me. The park/running lights work fine all around. The signal lights work fine all around. The hazzards do not work-anywhere-including the indicators in the dash. Most importantly the brake lights do not work on either side. The circuits on the signal switch check out OK and there is 11+ volts on the supply side of the brake light switch on the pedal. I thought I would be smart and removed the brake wire (red w/black stripe) from the signal switch connector and used a jumper to join that wire to the supply side of the brake light switch-but not only did no lights come on, my DMM showed a major voltage drop at the brake light switch supply/jumper connection. Argghhh! Any thoughts on where to look? I am a serious newby when it come to auto electrical circuits.
Postmaster
Joined: Apr 2000
Posts: 2,838
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From: SD
Re: brake light teaser
Originally posted by witt
there is 11+ volts on the supply side of the brake light switch on the pedal.
there is 11+ volts on the supply side of the brake light switch on the pedal.
Have you looked over the tech article about troubleshooting 70's brake lights?
Marty
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From: Washington
There are no flashers mounted directly to the fuse box but there are two glass cased flashsers wired into the harness in the same area. One seems to be the turn signal flasher while the other must be the hazzard flasher as it is where the wire comes from that supplies the brake switch at the pedal. The brake pedal switch does appear to work as it is an open circuit at rest and shorts when the pedal is depressed. I don't know how to check the flashers but I did remove them and place them in each other's place with no change.
I did print a copy of the tech article but it has not helped me figure this one out.
I did print a copy of the tech article but it has not helped me figure this one out.
Elder User
Joined: Jan 2004
Posts: 767
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From: Franklin, GA
Sounds like a bad brake light switch and/or possibly a fuse. If a blown fuse, replace it first then depress the brake pedal. If the fuse doesn't blow then check the brake light switch. If it does blow, you have a short down range in the harness going to the rear lights, possibly a faulty ground or bad bulb socket, or maybe even a hot wire in the harness that has had the insulation rubbed off and is contacting ground. Hope this is on track and can help you out.
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From: Washington
Well the fuses in the box are all apear OK with the test lamp lighting up on both sides of each fuse. The switch brake light switch at the pedal tests out OK, but just to make sure I wired the supply wire to the switch directly to the brake wire on the turn signal switch as it came out of the steering column - No change. Also, when I disconnected the supply wire from the brake light switch, it measured 11+ volts until I made the jumper connection I just mentioned. Then the voltage dropped next to nothing.
BTW - Thanks all for your help w/this problem.
BTW - Thanks all for your help w/this problem.
