Looking at the wiring diagram the only place where those two circuits come close to one another is in the fuse box. The fuses are next to one another. I would look there. Some of the fuses are coupled together. It's possible that someone tied the two together incorrectly. If not that than I'm with you that it's probably something in the dash.

John

New owener here, I was looking in the fuse panel and there are 3 visable relays, 2 of which are hooked together. Does anyone know which 2 SHOULD be hooked together, and how. (series or parallel) I've noticed for about the first 10 minutes of driving they work fine. But then the brake lights are on constantly, even after the car is shut off. I have an idea that for some reason pressure is building up behind the brake switch on the brake booster, and for some reason not being released. So the switch is seeing constant pressure, telling the lights to stay on. I don't like the wiring that has been done to it so I will be redoing that today. Looks like a new brake switch though.?

If you look in the Technical Resource Library you will find wiring diagrams including a diagram of the fuse box. The two large fuses on the right are tied together.

John

Page 15-10 of the shop manual shows the fuse panel. The feed to the top right circuit breaker (12 amps to light switch) is tied to the one directly below it (15 amps to stop light). The feed for these is on the left (towards the front of the car) and is black/ yellow stripe. The load wire on the upper is yellow/ red, and the lower green/ red.

Your problem is not electrical. The switch is a pressure switch that closes contacts when it sees brake line pressure. It is doing just that.

You have another thread describing brakes that stick or drag. Hmmm... Maybe your master cylinder isn't retracting. (Just like you described in the other thread.)

Brake fluid expands with heat. In a closed system, that causes the pressure switch to work. So, your electrical is confirming your suspicions.

When a Master Cylinder fully retracts, the reservoir is open to the brake line. Meaning, if you take the cover off the M/C, fill it with fluid, then go to a wheel cylinder and take the bleeder screw off, the fluid will slowly drain out. It has to be that way for shoe springs to retract. They force fluid back into the reservoir, so it has to be open.

First, I would find out why the M/C isn't retracting. You said you can lift the brake pedal and that would do it. Find out why it is binding. Leave all the lines on but unbolt the M/C, then look at your brake lights. The M/C has a return spring inside which pushes the spool back to the snap ring.

If that checks out ok, leave the M/C off and continue checking the booster and linkage. Get the mechanical problems put to bed first, then get into the electrical. Good luck. - Dave

Right, I think whatever the problem is, it is the cause of both issues. I think the heat causes pressure to build up, but then it won't release. Maybe a new M/C soon if I cant get it to release, the brake booster looks brand new.

Thanks for the input. I'll see what I can figure out.

This isn't hard... Crack the line going to the wheel that's sticking. That relieves any hydraulic pressure. Next, fix the back plate pads and springs so the shoes retract smoothly.

Then, make your M/C adjustments so that the piston returns.

Now, git to git'n! - Dave

Got to mess with it on Sunday before leaving town for the week. It IS the M/C.. It has a new switch, and new booster, but old MC. I drove it long enough Sunday for the pressure to build up tight enough to where the rear wouldn't even release when I pulled on the pedal AND the lights wouldn't go out.

More to come once I'm home this weekend.

I recommend replacing it with a dual master if you haven't already done so. That is always my first modification to an old car with a single.

Aside from the usual hydraulic modifications and push rod length issues, on the 64 you would have a conflict between the diagonal brace and the cover on the dual master. I solved this by cutting a notch out of the cover, then using a small piece of sheet metal, bending it and trimming it to cover the hole. I used solder to make it liquid tight and then painted it semi-gloss black.

Here's a picture with the brace removed.

I don't get it. One set of shoes and a tire was destroyed from overheating:

Why destroy another set and possibly warp the drum or cause further damage? Stop driving it until you get a new master cylinder installed and adjusted properly. - Dave

I wasn't the one who did the damage to it the first time around. You can tell when the brake starts causing trouble, and for the most part you can make it release. That was the first time it has locked up on me, and I was already back in my driveway so no harm done. But it is parked until I can be home long enough to replace it.

Just ordered a master cylinder rebuild kit from macsautoparts.com ... Stay tuned for an update!

Dylan, I am particularly interested in how you adjust the booster's adjustment rod, explained in the shop manual (Section 10-2, Push Rod Adjustment). Let us know when you get to this step. - Dave

Can someone get me a link to this? I can't seem to find it. I'm New, I don't know what to do!!