USAsOnlyWay

Update
So I was able to get home last weekend and work on the car some, it is definitely not the switch. When I supplied power directly to the light board the lights lit up. Meaning to me I must have a grounded out the "power" (+) wire which is shorted out every time I brake...?

Also, as an FYI. I have a correction to the general knowledge about Early-86s and who knows what other years. (The other posters may be correct for their respective years, so I can only say I've found this with an early 86.) The lower tailights and the high mount stop lamp are on the same "internal switch", not on a different "internal switch" as previously reported. Correct there are two plugs on this pressure switch (in addition to an entire other pressure switch working with the brake pedal, a vacuum release switch/valve for the cruise control) and one is for brakes and the other for cruise control.

The brake light pressure switch has a connector coming perpendicular off the switch body and then one connector at the back. The side connector has three wires coming out of it, Orange, White and Blue. This connects through two terminals (Orange on one, White and Blue on the other.) The Orange is hot (+) and the circuit is completed with the White/Blue connector when the brake pedal is depressed. The white wire goes to the lower lamps, the blue wire to the upper lamps. For the white wire to get voltage the blue wire must as well as they are both connected to a single blade in the switch, the only way for them to not both get power with a good switch is for there to be a problem in the connector, which seems very rare. (Additionally upon depressing the brake and grounding to pin A (ground) in the ALDL connector, both get voltage when the pedal is depressed and none when not-depressed. I did take apart the switch to inspect this and verify there is only one switch for both wires.

The second plug/"switch" on this switch is at the rear of it and has two smaller blue wires, these are part of the cruise control and upon depression of the brake pedal the circuit is broken which disengages the cruise, this runs through the clutch switch for cruise as well.

I have confirmed both of these visually, electrically and in the service manual. The problem is not in the switch!

I am not looking forward to taking out all of the interior to get to the wire loom that runs to the roll bar but if the manual is correct it appears to be running through the passenger compartment.

Additionally I did run 12 volts directly to the white and blue wire and the white wire resulted in lower tailights working, the blue wire...nothing


I have an 86 which the center high mount stop lights on the hatch above the integrated roll bar. I changed the lamps a month or so ago...and bam, now they are all dead. I checked the bulbs and they are good.

I'm thinking I'm going to have to take off the plastic halo pieces to try to check the wiring, but where does it go after that? Any ideas on what side?

I'm just curious if anyone has experienced this before?

I have the RT S/T Frame roll bar, which is going to make it a royal PITA so I thought I ask the collective first.

Have a good one.
Thanks

JonnyAngle

1. Get out your Multimeter.
2. put it on the 20v setting, and put the probes in the CHMSL plug.
3. Hit the brake, if there's power there, then the problem is in the light housing connections.

If there's not power, it's PROBABLY a poor ground. So, repeat the steps above but use a different known ground, instead of the ground on the CHMSL plug. Then re-ground the CHMSL and it should work. Let me know if you have any more problems.

USAsOnlyWay

Hmm, like a local re-ground?

Not a bad idea. Though I hate adding to the previous owners "rat nest" style wiring.

I already did the test. No power coming though. I should have said that I suppose.

I can't remember if I tried with another ground, I'll try that.

Thanks

JackDidley

Brake light switch on the pedal. Its a black one. The other is for cruise. The one for the brake lights actually has 2 switches inside. Thats why the lower brake lights still work. Its only about $10 and real easy to change.

AGENT 86

Aurora40

Common failure.

USAsOnlyWay

And this is why I ask! Nice.

I won't be able to get back into it until the weekend after next but I'll update this thread once I do.

Thanks again!

USAsOnlyWay

I put an update up above and unless I have a very very hack-jobbed Corvette...VERY POSSIBLE, in my 86 the upper and lower brake lights are on the same switch. More details above.

Note: I only get to work on this car about once every 2 weeks if not more infrequently. I'm trying to slowly fix up the rat nest I purchased so I apologize for the delay between postings.

bad-zr1

You mentioned that you have a frame roll bar, is this one that mounts to the stock seat belt top bolts? If so there is a good chance that when installed it pinched or cut the wires on the passenger side. I installed a harness bar and just removed the seat belt bolts and reinstalled them with the bar in place. The wires are so close to the bolt hole that when I put the bolt back in on the passenger side it cut one wire out of a bundle of 5 or 6. You guessed it, the CHMSL no longer worked. You have to take off the side panel and light to fix it.

USAsOnlyWay

Interesting, thanks for the insight!

So you are referring to the upper seatbelt mount or the lower? I think by harness bar, you mean upper. Mine is a weld in 4pt cage and thus I didn't touch this, I did however touch the bottom one which is where I believe the harness also runs. Something definitely worth checking out.

Thanks!