Turn signals dont work when the headlights are on.

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david lucka

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I just bought the truck yesterday and last night i was driving and realized that the turn signals dont work when the headlights are on. And i also realized that when the headlights are off and i have the left blinker on both lights flash in the rear. It does have aftermarket tail and headlights, im not sure if someone maybe wired them in wrong. I just need all the help i can get.
 

89RCLB

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Start with checking the ground at the end of the left frame rail
 

RichLo

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Yea, grounds are always a good place to start and while your checking, look for any hacked wiring or pinched/corroded wires.
 

david lucka

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Start with checking the ground at the end of the left frame rail

Yea, grounds are always a good place to start and while your checking, look for any hacked wiring or pinched/corroded wires.
Okay. Yeah, I just checked the grounds and I disconnected them and redid them to make sure they had a good connection and it didn’t do anything. One think I did find while I was under there was a bunch of wires that they just have had to change in order to put the other lights in. I’m
Not sure though.
 

someotherguy

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Usually aftermarket lights are a plug-in situation. If someone's been in there playing with the wires...who knows why. If it has a trailer harness connected, take it out for now to simplify your troubleshooting. They can commonly cause problems especially if they did a crummy job installing it.

In that same general area at the end of the driver's frame rail where you found the ground wire for the rear lamp harness (there actually should be two - one for the main harness and one from the tag lights, may vary depending on year) - there's also a disconnect point for the harness. Pop it loose and use your test light on the side coming from the truck, so that you can isolate the aftermarket lamps and any questionable wiring.

The colors are as follows - brown is tail/running lights. Yellow is left turn/brake. Dark green is right turn/brake. Light green is reverse.

Richard
 

david lucka

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Usually aftermarket lights are a plug-in situation. If someone's been in there playing with the wires...who knows why. If it has a trailer harness connected, take it out for now to simplify your troubleshooting. They can commonly cause problems especially if they did a crummy job installing it.

In that same general area at the end of the driver's frame rail where you found the ground wire for the rear lamp harness (there actually should be two - one for the main harness and one from the tag lights, may vary depending on year) - there's also a disconnect point for the harness. Pop it loose and use your test light on the side coming from the truck, so that you can isolate the aftermarket lamps and any questionable wiring.

The colors are as follows - brown is tail/running lights. Yellow is left turn/brake. Dark green is right turn/brake. Light green is reverse.

Richard
Okay. I’ll probably do this tomorrow because it’s snowing here right now. But I’ll let you know what I find if I find anything. I also have a headlight out now too. I’m hoping it’s just a burnt out bulb though. Thanks.
 

Eveready

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Sounds like there might be a short somewhere if both sides activate at the same time for any reason. Definitely follow the advice above re any old trailer hookups and grounds. It would help if you had a set of stock lights to temporarily hook up and see what it does. Right now you have too many variables and need to narrow those down.
 
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david lucka

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Okay, I went under and took a look at the wiring. There were A LOT of extra wires that really there was no reason for. So I eliminated those. But I found out that the problem isn’t in the back. It’s somewhere towards the front. Because I disconnected the harness leading to the lights and went to the single output from the front and there still wasn’t power when there should have been. I was wondering if maybe the headlight switch could cause it. Because there is also the passenger side headlight that doesn’t work. The bulb isn’t burnt out though. I also tested the brake lights alone and connected them straight to a battery and they worked good
 

someotherguy

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The headlight switch and headlights won't have any effect on the brake or rear turn signals, only the park/running/tag lights.

The headlight assembly on either side has its own ground, so check that. Single black wire, its termination point varies depending on year and model but you'll find it attached very near the headlight, usually on the core support.

Richard
 

david lucka

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After a ton of hassle i finally fixed it. Something was wrong with the ground in the back, but it was tricky because i had to completely move it in order for it to work. It was connected to the receiver hitch which then connected to the frame and i think the connection between the hitch and the frame was bad.
 
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