Hi all. I have a 1981 4-speed car that keeps blowing the brake light fuse. It doesn't blow it as soon as I put a new one in but typically, at some point during my 1 hour commute to work, it will blow the fuse which makes it really hard to troubleshoot. It doesn't always blow it but most days it does. I've looked at a wiring diagram for a 1981 but something doesn't seem right because it shows that the brake lights, hazard lights and headlight warning buzzer are on the same fuse but on my car, the orange wire to the seat belt warning buzzer is hot even with the fuse pulled out. It makes me wonder if there might be something else on my car that runs through the brake light fuse. It never blows the turn signal fuse so I don't suspect the wiring from the turn signal switch to the actual brake lights and I'm not running the hazard lights so I don't suspect that circuit. I've looked at the wiring from the brake light switch to the turn signal switch and it looks okay. I've removed the headlight warning buzzer just to remove it from the equation but as I said, I don't think it is on the brake light fuse anyway and it still blows the fuse with it removed. I've looked at the wiring at the back of the car to look for any bare metal wires or any reason why it might be blowing the fuse but I don't see anything. Does anyone have a wiring diagram for a 1981 that doesn't have the headlight warning buzzer on the brake light fuse? Or one that has something in addition to the brake/hazard/buzzer on that same fuse.

 

Could be the harness contacting the frame when driving. Remove fuse and insert a test light across the fuse terminals ( mine has alligator clips). With key on test light should be off. Start wiggling the harness as you work your way along it. The test light will glow when the harness “finds” a ground

 

After my last round of looking poking and prodding of the wiring harness under the dash and at the back of the car, the fuse has not blown in 2 days. If/when it does finally blow again I can try what you suggested and see if I can find anything.

 

My favorite way of diagnosing these scenarios is ordering all new electrical for the car. Why take chances?

 

I finally found a chafed spot where the harness goes up to the turn signal switch and was able to fix the problem.