I recently picked up my first 911, a unique 78 SC (continental orange/orange interior). I'm wondering if all these problems are related, and I'd appreciate any insight before I dig into the wiring.

When I got the car, the brake lights and turn signal lights did not function (no flashing lights at any corner and no sound from the flasher, no nothing). The reverse lights worked. I decided that the brake light switches on the master cylinder were bad. When I took a close look, I saw the master cylinder was leaking brake fluid down the booster stripping the paint off it. That lead to a lengthy project for another thread. Anyway I replaced the master cylinder, which came with new brake light switches installed. When all was back together, I was delighted that upon first testing, the brake lights worked. In addition, the turn signals came to life at the same time (I don't know why.). Reverse lights still worked.

During a long drive last weekend, I noticed that the turn signals were not working all the time, but this time, there was an intermittent buzzing sound from under the dash when the signal was activated instead of the normal click, click when they work properly. Is this a bad relay or flasher? Should I suspect the steering column switch?

Also, the brake lights are not working all the time, now. It seems that when the brake lights work, the turn signals also work properly, and when the brake lights don't work, the turn signals also don't work. Does this make sense? The problem is with both tail lamps at the same time. Never just one.

Also, the car has cruise control. Initially, stepping on the brake deactivated the cruise control as it should, but later in the drive, it took several increasingly hard steps on the brake to deactivate the speed setting. And, later, it would not deactivate even after substantial brake application. That was a little disconcerting so I quit using the cruise for the rest of the drive. Is this related to the brake lights not working? Of course, I was driving and could not tell if the brake lights also weren't working when the cruise control wouldn't deactivate.

Other notes. The emergency flasher has always worked. All four corners flash properly even when the turn signals aren't working. So I suppose the flasher is fine (if the circuits use the same flasher).

I did a transmission gear oil change, and afterward, the reverse lights no longer worked. There was some linkage and a loose hanging tube in the vicinity of the fill plug. I knocked them around a bit as I wrenched out the plug. Could I have done something to the reverse light switch or the linkage that operates it?

Thanks for any help.

Brett

 

Brett: Your car has the turn signals, cruise control, both brake lights and the turn signal flasher all on the same fuse. It should be 16 amp (red), and you will have to pull it out. Sometimes there is just enough corrosion that you can't see, or the wire on the fuse is broken but can touch. It is the 11th fuse from the dashboard end of the fusebox. Replace that fuse and you should be set. However, you still might have a problem with the cruise control - check the engine compartment cable where it connects near the throttle body. Sometimes the plastic end can break and the cable can get stuck, which prevents it from releasing the throttle. Good luck!
Pete

 

Thanks for your response, Pete. I'll just replace that fuse to start with.

Brett

 

I had looked over the fuses briefly and nothing was blown, so I didn't think more about it. But, I pulled the old fuse in question, which was quite old and plenty oxidized on the surface, sanded the contacts, and installed a new one. Voila, brake lights, turn signals, and reverse lamps all worked. I easily forget that this car is 26 years old, since it's in such good condition (44,000 miles). Who knows how long it's been since some things have been changed.

I hope this was the real culprit. I really hate tracking electrical problems.

Thanks for getting me back to basics on this one.
Brett

 

Good news! I'm sure that's the problem...

Pete