Brake lights not working

[rickjames8]

Hi All-

I just delivered my car to the new owner in PA. It was nice to have one final road trip with the car.

My wife followed behind me and called me on the phone at one point saying that it didn't look like the brake lights were working all the time. Then, for the last half an hour, they didn't work at all.

A few days earlier someone said they thought it looked like they weren't working, but after checking them in the garage that evening, everything looked fine and I assumed this person was mistaken.

My gut is telling me that this is the brake light switch, as it's affecting both sides and the 3rd brake light (which is tapped in before the tail light boards).

I was going to clean up the switch when I arrived, the same as I've needed to clean the door pin switches when they were acting up, but the brake light switch seems to be a sealed unit. It is possible to clean? Is it a likely culprit here? I'd like to refund the buyer the cost of the repair as I'd like to deliver the car as it was described in the ad.

-Rick

[mr_maxime]

Check the bulkhead connector in the engine bay. I've had wires come loose before.

[Ron]

You can just jump the two wires going to the switch together to check it..

[DMC5180]

You can just jump the two wires going to the switch together to check it..

+1

More importantly make sure one one two wires to the switch is live with the key On. If that checks out and you still don’t have lights, check the connection where the 3rd light was tapped into the wiring. Especially if Scotch lock wire taps were used.

[Ron]

+1

More importantly make sure one one two wires to the switch is live with the key
fwiw, it is fed via Fuse 18, which should be live at all times.

[DMC5180]

fwiw, it is fed via Fuse 18, which should be live at all times.

Depends on the VIN.

Some cars have a fuse 18 while others don’t. Those have an inline fuse located about where your right elbow rests, under the center console. The latter version is key switched.

Given the intermittent nature of the OP description before total failure, I doubt its a fuse issue though. But anything is possible on these old cars.[emoji6]

[Ron]

Under the console?? That sounds like an improvement. lol

[DMC5180]

Under the console?? That sounds like an improvement. lol

Yeah, no kidding. It was a rolling production change. I don’t think anyone knows when it took place though. My car has the inline fuse.

[David T]

Yeah, no kidding. It was a rolling production change. I don’t think anyone knows when it took place though. My car has the inline fuse.

My vote is for the taillight boards and bulbs. Because of the intermittent nature of the problem it tends to be bad connections. I agree to start at the brake switch to "divide and conquer". Wherever the power comes from it has to be on the switch. Once you verify you have power at the switch you jumper it and see if you can get the brake lights to light up. Don't forget, just because you have power at the taillight boards (if in fact, you do), you also MUST have a good ground to complete the circuit.

[Josh]

My vote is for the taillight boards and bulbs. Because of the intermittent nature of the problem it tends to be bad connections. I agree to start at the brake switch to "divide and conquer". Wherever the power comes from it has to be on the switch. Once you verify you have power at the switch you jumper it and see if you can get the brake lights to light up. Don't forget, just because you have power at the taillight boards (if in fact, you do), you also MUST have a good ground to complete the circuit.

X2

a somewhat common issue with our cars.

[mr_maxime]

X2

a somewhat common issue with our cars.

One reverse connection was bad on my old boards which caused both to sides not to work.

[DMC5180]

Flaky boards is a common issue, no doubt. But he’s lost all brake lights including 3rd eye assembly.

[David T]

Flaky boards is a common issue, no doubt. But he’s lost all brake lights including 3rd eye assembly.

Which is why I mentioned the need to have a good ground for the circuit to be able to be complete. Right now the first thing to do is verify 12 volts at the brake light switch and then jumper it (if you do have 12 volts on one side) and see what happens.

[DMCVegas]

This is a perfect example of how repairs become exceedingly difficult and expensive due to a lack of structured troubleshooting.

While there are any number of reasons as to why your tail lights might not be working, you can't just randomly hope that one of them is the problem and that there is always going to be an instant fix. You'll waste more time and money that way. You could have bad tail light boards, yes. You could also have a bad brake switch. Hell, you might only have an improperly installed & configured brake switch because of incorrect tinkering due to a PO. It's uncertain. A misadjusted brake switch can cause this exact issue. The switch is always closed, and doesn't break it's connection until the button is actually pressed. It's wired opposite from what you normally expect from a button. So with your foot off the the brake pedal, the button is pressed in. Once you press the pedal down, it's arm lifts up off of the button to close the switch and turn the brake lights on. The switch is supposed to be tensioned properly so that as soon as you bump the pedal it makes contact. If someone screwed that switch all the way down, it will appear to cause an intermittent brake light issue. Pressing the brake pedal lightly while going slow doesn't force the pedal down far enough to turn the rear lights on. But pressing hard for quicker stops from faster speeds will result in the driver pressing the pedal harder, and will in turn then turn the brake lights on. Thus the issue appears to be intermittent in appearance.

But here is the best way to quickly test your brake light system. You're gonna need a multimeter. If you don't have one, get one. If you don't know how to use it, that's okay too. There are plenty of YouTube videos, or you can just post questions here. But I guarantee that if you follow this structured troubleshooting list below, you'll have your issue fixed in no time. This is how you should always go about repairing a problem instead of just shotgunning it each time.

Step 1 Using an separate, independent ground, check for the presence of 12V at the switch.

Is there Power (NO) -> >>>STOP<<< Check your fuses & repeat Step 1.
(YES) -> Proceed to Step 2.

Step 2 Check the switch for internal continuity.

Does the switch close as soon as you press on the pedal? (NO) -> Proceed to Step 3.
(YES) Proceed to step 4.

Step 3 Adjust the switch by backing it out and letting the button slide out until it closes. Then screw back in just past the point where the pedal pushes in to trip the switch and break the connection. Once you have adjusted the switch to close as soon as you press on the pedal, proceed to step 4.

*Note: If the switch entirely dead and doesn't respond at all-> >>>STOP<<< Replace Stop Lamp Microswitch (part #100820) and repeat Step 3.

Step 4 Disconnect the wires from the brake light switch, and insert a jumper in between to deliver a constant 12V to the rear brake lamps. Using an separate, independent ground, check for the presence of 12V within socket connections for the Rear Tail Light Circuit Boards.

Is there Power (NO) -> >>>STOP<<< Inspect wiring & bulkhead connections, and reseat/repair as needed. Once complete, repeat Step 4.
(YES) -> Proceed to Step 5.

Step 5 Check ground connections within socket connections for the Rear Tail Light Circuit Boards using the verified 12V source.

Is there Ground (NO) -> >>>STOP<<< Inspect wiring & bulkhead connections, and reseat/repair as needed. Once complete, repeat Step 5.
(YES) -> Proceed to Step 6.

Step 6 Remove Tail Light Circuit Boards, and test for continuity.

Is continuity verified? (NO) -> >>>STOP<<< Replace boards if original, or repair later versions.
(YES) -> Replace light bulbs.

[outatym2001]

A big THANKS to DMCVegas for including the trouble shoot guide for non-functioning brake lights.
I have an early VIN, July 1981 build and there is no fuse and no wires at position 18 in the Fuse Box. I removed the center console and could not find any inline fuse.
My digital multimeter showed I had 3 volts going to each bulb in the brake light circuit.

I used Lime A Way in the green bottle and a slender nylon bristle brush to clean the metal contacts at the bulkhead connectors in the engine compartment.
Then rinsed with water.
Then sprayed the metal contacts with Electronic Cleaner to displace the water.

The black connector is the wiring harness that provides electricity to all the rear end light bulbs.
Now my brake lights work and I can drive the D. Yeah!

Edit: I found the inline fuse for the brake lights. It’s located under the left side dash board just above the clutch pedal. It’s a 25 amp glass fuse. BUSS AGC 25. 32 volt.
Attached to the fuse holder is a green wire on one end and a brown wire on the other end.