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Taillights/Tag lights out

Discussion in 'Electrical & Audio' started by 79dentside, Dec 11, 2019.

  1. 79dentside

    79dentside Full Access Member

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    Any ideas? Both taillights and the cab taillight are out, as well as the tag lights.

    Blinkers, brake lights, and reverse lights all work. Headlights work, dash lights work.

    I cut back the grounds/stripped back the wires and regrounded them with new connections. Didn’t help.

    thanks!
     
  2. Dmack

    Dmack Full Access Member

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    You might try checking for power in the circuit at the rear harness connector . That would eliminate the wiring from there to the lights. Then work forward or back from there depending on what you find.
     
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  3. 79dentside

    79dentside Full Access Member

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    well I’ve been working on the truck in general all night, including this issue. I found some cut wires, so I I re-spliced them.
    [​IMG]

    [​IMG]

    Also re-did the grounds only to find nothing is getting power, taillight/plate light wise.

    It’s gotta be up front. Headlights do work. Any ideas? Thanks!
     
  4. Frankenchevy

    Frankenchevy Supporting Member Supporting Member

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    Do the front running lights work? If you only pull the light switch half way do your front markers light up?
     
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  5. 79dentside

    79dentside Full Access Member

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    Yes they do. Both headlights and running lights work.


    Thanks for the help!
     
  6. Matt69olds

    Matt69olds Full Access Member

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    With the headlights on, check for power on the brown wire at the bulkhead connector. The brown wire is the tail light feed. Lay a brick on the brake pedal, check for power on the dark green and yellow wires, those are power feed to the brake/turn signals. Light green will be the backup lamps. If all this checks out, start working your way back.


    Chances are your looking for your problem in the right area. The problem with these trucks is entirely too many people have had their hands on the tail light harness, making their own “repairs” while fixing a previous owners “repair”. I usually plan to just cut out everything from about the rear leave spring mount back. That’s usually where the factory wiring is still intact. If you see wire nuts, butt connectors, scotch locks, or the cheap 59 cent a roll electrical tape peeling off corroded wire splices, keep going forward.

    I have a salvage yard that lets me wander the wrecks, whenever I see unmolested Chevy truck tail light harnesses, I cut them out of the truck for occasions just like this. You can easily modify the square body taillight lenses to accept to 3057 bulb and sockets, or depending on the year it may still use the older 2056/2057 bulbs.
     
  7. chengny

    chengny Full Access Member

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    The headlights are on a separate circuit. You are concerned with the BRN 9 circuit. It supplies the parking/marker lights (both front and rear) as well as the tag lights.

    The BRN 9 circuit originates at the H/L switch and runs straight to the cab side of the firewall connector block. There are two lighting sections in the main connector - one for the front and one for the rear.

    The BRN 9 from the H/L switch is first run up to the front section. At that point there is a jumper that is spliced on to it - and that jumper goes over to the rear section.

    If you are getting power to the front lights on BRN 9 but not the rear lights, its a good bet that the problem is with the jumper. Its probably only about 6 inches long and is hidden behind the fuse block. Maybe the images below will make things clearer. The first one shows the cab side of the bulkhead connector and the lower one shows the two wires entering the engine compartment:

    Cab to fb.jpg


    In the engine compartment:

    eng side.jpg

    To access the jumper wire you will need to move the fuse block aside. It is secured to the firewall with two bolts - one in the upper RH corner and one in the lower LH corner. Back the bolts out (actually they're more like screws) and the fuse block will be free to move - to a certain extent. But there should be enough slack in the wiring harness to allow you to inspect/repair the jumper.

    3rd 1980 StyleFuseBlock-Front3.jpg
     
    Last edited: Dec 12, 2019
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  8. Craig 85

    Craig 85 Full Access Member

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    A big issue I see is that a PO has added 2 trailer "T" connectors (Red arrows). Remove these from the set up and plug the two yellow stars together. I know when I bought my truck the original "T" connector went bad and I had to replace it.

    79 trailer plug.jpg
     
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  9. 79dentside

    79dentside Full Access Member

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    Oh my gosh, THANK YOU! I will check this out tonight!!!


    I actually removed that “T” last night for the trailer lights. I depleted the trailer lights until I fix my lights. Less variables in the mix for the time being. Good catch.
     
  10. Dmack

    Dmack Full Access Member

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    My record was finding 21 splices in a 5 wire rear harness in an f350. Surprisingly I was having taillight problems.
     
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  11. 73c20jim

    73c20jim Supporting Member Supporting Member

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    Rear lights have their own ground.

    Check that.
     
  12. 79dentside

    79dentside Full Access Member

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    So I pulled the fuse box, I am lost... I don’t see anything problematic, but then again it is too shallow for me to get anything in there. I felt the wires because that’s all I could do with the space I had, nothing is chaffed or disconnected.
     
  13. 79dentside

    79dentside Full Access Member

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    After putting the fuse box back in, I hooked up the battery and gave the chassis a once over. Crawled from the rear all the way to the front tires looking for damage.

    I gave up until I turned on my lights... I must have jostled something when messing with the fusebox. What the heck. These have NEVER worked.

    [​IMG]

    Mystery still resides, why my rear wires were cut?? Oh well, I rewired it and put a new ground on.

    Thanks for the help, now we know it is indeed up front! The plate lights don’t work, I am gonna put bulbs in first, then see if something is up with the wiring.
     
    Last edited: Dec 12, 2019
  14. chengny

    chengny Full Access Member

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    I gave up until I turned on my lights... I must have jostled something when messing with the fusebox. What the heck. These have NEVER worked.


    I bet that is exactly what happened. I also bet that eventually the problem will return - but who knows, maybe it won't. Wait and see. I always live by the old adage; You don't need to go looking for trouble, usually it will find you.

    On the plate lights; be sure the housings, fasteners and landing areas on the bumper are clean and tight. Unlike the other lighting, those lamps are grounded through their housings. There is no ground wire:

    Pages from ST_352_79_1979_Chevrolet_Light_Truck_Wiring_CK_10_30_Only[1].JPG
     
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  15. 79dentside

    79dentside Full Access Member

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    Agreed, I don’t think I “fixed” anything. For the time being, I will be able to drive it at night if need be, but if/when this problem comes back, I know it is up by the fusebox. This is all the distance I could get without straining the wires... maybe I’m missing something, but the harness wires didn’t have a lot of slack.
    [​IMG]

    My concern is when I actually do have to fix the wire (I assume it’s the jump wire we were talking about?) I may have issues getting in there.

    I will dig into those plate lights too. Maybe something is cut on those as well that I missed haha.
     

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