SC Brake Warning light problem

[universeman]

All,

I rebuilt my parking brake handle with a new switch last year. For a long time, that seemed to fix the brake light in the dash; worked like it should.

However, it started doing something odd, during hard driving it would intermittently come on. I know some have said that the alternator / voltage regulator can cause it to do that, so I suspected that to be the issue. Kept resetting the circuit using the key method.

Now, it has gotten worse. Stays off permanently when car is running (but does go on when key in "On" position.) If I touch the cruise control switch (up or down), it goes on and stays on until I reset the circuit.

Any ideas on how to troubleshoot this? I have the wiring diagrams but I'm not so good at figuring out what they mean. Cruise control does not seem to work (I had it rebuilt recently also, and it used to work. Now all it does is turn on the brake warning light )

Thanks all!

[tirwin]

Do you have a voltmeter in the car? If not get a $10 Innova cig lighter unit from Amazon. Voltage spikes are of course the telltale sign of a VR problem. You're also more likely to see voltage spikes during hard driving.

[universeman]

Thanks tirwin, I'll give that a shot. I'm really thinking the problem lies elsewhere however -- now the light comes on any time I give the cruise stalk a nod up or down. That to me says some kind of circuitry problem. Worth $10 to monitor it for a while though...

I thought maybe the issue had to do with the below (see pic) - I took the taillight housing out to rehab it...and there was 3/4" deep dirt in the housing, apparently it all got thrown in by the rear wheel via the wiring hole, whose boot was not seated in the hole. Amazing that so much dirt could get in, covering the contacts, etc. Cleaned it all out BUT the brake light contact board was loose in its holder, and messing with the little tabs that hold it in only caused one to break. I was able to secure the board with some tape and by using some foam strips behind the board, which when compressed by the housing cover held the board tight against its holder...however I wonder if the board was breaking contact with the bulb during spirited driving and causing a fault. Anyone know whether or not this would cause the brake warning light to come on?

[timmy2]

Brake warning light will come on if a bulb comes loose.

[Jdub]

Isn't that gravel a mind-blower? My rear lights were fully sealed - but the crap on top of the assembly and all around it - just bad news.

Removing and cleaning up the rear light assemblies, including re-sealing, cleaning up the reflective area and re-seating the bulbs is a must. When I did this I made sure to douse with water and then double wax the area around it. Good insurance!

[universeman]

Back to the brake warning light...

I removed the light module from the dash (procedure: pop off red lens, remove clock and unwire, reach through and push on back of module while gently prying retaining clips inward from front opening of module).

It had some light corrosion on the contacts which I cleaned off. Behavior did not change when I plugged it back in.

So I unplugged it and tested it with a circuit tester. Contacts 15 and 30 are getting power in both the handbrake up and handbrake down position, and moving the cruise stalk does not seem to light up any other contacts with 12v power. Hmmm. According to Bentley, the 30 contact is supposed to stay hot all the time and the 15 comes from the oil temperature indicator, and is a red/blk wire that appears to be a common or bus for all the gauges in the dash including boring things like the fuel reserve light. More testing to come.

[tirwin]

Wow! That is a crazy amount of dirt in that housing.

Good idea to clean the contacts and grounds. I have replaced many of the wire terminals with insulated connectors. It is amazing what a difference it can make.

VR problems can be crazy. I was having the same symptom with the parking brake light coming on. I also had problems with the radio cutting out. (Apparently there is protection mechanism built into the aftermarket radio that shuts it off when it detects a voltage spike.)

I pulled the alternator and had a local shop test it. They claimed it was fine. I was worried that it could've been the beginning stages of a failing VR. Thinking that I'd rather not do the job twice, I ended up getting a new one and problem solved.

I have chased many electrical gremlins and I think (fingers crossed) I have finally squashed them all. Shorted fog light wire, previous owner hacks, cracked fuse panel that caused loose fuses to intermittently break contact in the fuse holder, bad grounds, corrosion, etc. It is a pain but the results are worth it. The final pieces to the puzzle were the new engine and CIS harness that timmy2 made for me and replacing the factory fuse panels with Fred Cook's ATO style.

[universeman]

Pictures of the inside, for the curious...
Any ideas how to test this circuit board?

[tirwin]

I'm pretty sure there is a thread about the circuit board. I think the module is NLA. I can't remember who started it but they went through an explanation of it and diagnostics. A search should turn it up though.

I can't tell from the pictures you posted but is the bulb replaceable? I seem to remember that it is soldered in or something crazy like that.

[gomezoneill]

I thought I read a post a while back that the two brake light switches on the master cylinder could cause the light to come on.

[universeman]

Another update
Disassembled my parking brake lever (ugh) again
Appears the little spring piece that is clipped to the handbrake has broken again
I just replaced it a year ago...what a bummer
Have to re-rivet a new piece on there in order to get my brake switch working again.
Design of this part seems to be flawed, this is the second broken one I've had! Maybe adjustment is off or...

[universeman]

Bulbs are replaceable, they just pull out. Similar to xmas tree lights, glass base with little wires bent back. Just fit in the slot.

I took the board out, hit it with contact cleaner and got all the corrosion off. There did seem to be some communication of current between two of the leads (30 and K, which you can see in the picture.) I'll post a pic of the cleaned up module. That stopped the cruise stalk issue (yay!) but does not yet help me with the handbrake, whose switch is broken. I'm being very careful with the module now that I know it's NLA!

[timmy2]

Any continuity fault of high resistance, a ground or an open anywhere in the brake light system will cause the light to go on.
MC switches, lamps in sockets, handbrake, cruise control module, wiring...(edit, never mind, just saw your last post)

Did you unplug the cruise control plug to see if it went away?

The other thing to note is the relay will latch until you disconnect the battery, so even if you fix the problem the light still comes on until you kill power to the car.

[universeman]

another pic after I cleaned up the module. You can see the corrision is much less evident. Light would work if my handbrake contact bow (that's what it's called if you're searching for it on PP) hadn't broken. I think this problem may be fixed.

[universeman]

Thanks Dennis, good to know! I'm going to fix my handbrake contact and see if the problem goes away (and stays away)! Will keep this thread updated for others.

[universeman]

Just this morning, after fiddling with the heater levers, I found that my brake warning light isn't working again. Drove off with the brake engaged.

AAAAARRRRRRGGGGGGHHHHH

I suspect the contact bow is broken again. Using the contact adjustment screw (accessible without removing the entire assembly) did nothing. Can't figure out what's causing this? Has anyone else had this piece break on them, ever? Why would mine break every few months - can't figure out what it might be catching on?

[universeman]

Update on this: parking brake switch assembly wasn't broken, but needed another adjustment. There is a rubber piece that goes on the inside of the brake lever that functions as a stop when the lever is down - that's an important piece to have and mine was missing (plus it cushions the handbrake lever when you release it which is nice.)

It's also crucial that you adjust your parking brakes so that it's 4-5 clicks max before they're engaged. Too much more than that will break the contact bow -- it goes down and hits on stuff in the tunnel if you raise the handle too far. Over time it weakens and breaks.

[DRACO A5OG]

Good Job! Brother Jason!