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Thread: Brake lights not working

  1. #11
    Senior Member mr_maxime's Avatar
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    Quote Originally Posted by Josh View Post

    a somewhat common issue with our cars.
    One reverse connection was bad on my old boards which caused both to sides not to work.

  2. #12
    Senior Member DMC5180's Avatar
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    Brake lights not working

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

    VIN 5180, Frame 3652, STAGE II​, DM-eng Solid State Solutions (RPM Rly, Dm.Lt.Mod., Fan Fail Mod. , FAN Rly, HS.Rly) , HID headlights, SPAX user since 2009, Eibach springs, M Adj. Rear LCA's, DPNW poly-sway bar kit, DMCEU LCA Stabilizer link kit, DMCMW Illuminated door sills, Aussie Illuminated SS Shifter plate, REAL MOMO EVO Steering wheel, DELOREANA Extended View Side Mirrors w/ Heaters, DELOREANA LED Door Lights.

  3. #13
    Senior Member
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    Quote Originally Posted by DMC5180 View Post
    Flaky boards is a common issue, no doubt. But heís 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.
    David Teitelbaum

  4. #14
    Senior Member DMCVegas's Avatar
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    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.

    Wake me when hockey season returns...

  5. #15
    Senior Member
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    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. Itís located under the left side dash board just above the clutch pedal. Itís 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.
    Mark Vanyo
    Links to DeLorean related web sites!

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