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2015 GMC Sierra 1500 headlights won’t come on

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I’ve seen similar topics posted around the internet but no one came back to say how this issue was resolved. 
 

One light burnt out about a week ago. I finally went to change it today and noticed the other was out. Got new bulbs....still won’t turn on. Changed the fuse and nothing. Swapped relays around and nothing. Checked the plug with the lights in the on position and only reading 7v both sides. Battery ready 14+v while on. Don’t know why it’s only getting 7v at the plug. Any ideas?

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12 hours ago, Lsgun1 said:

Check grounds

I'm fighting the same issue this morning. 

 

Where can I find the gounds for the headlights? Without crawling all over the truck and chasing wires (in the rain today).

 

TIA

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You can search for a wiring diagram or just follow the harness back and see where a black wire pops out and bolts down to something. The battery ground cable seems to be the most common problem with anything electrical on these trucks.

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19 minutes ago, Lsgun1 said:

You can search for a wiring diagram or just follow the harness back and see where a black wire pops out and bolts down to something. The battery ground cable seems to be the most common problem with anything electrical on these trucks.

Thanks. Been googling for wiring diagrams and haven't found anything very good. Have any favorite links you use?

Got a multi-meter at lunch (couldn't find mine this morning). Will be crawling all over the truck this evening.

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I haven't had to search for anything to repair yet. There is probably a link to the service manual on here someplace.

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Looks like the BCM is the ground. What do you have for voltage at the fuse?

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Ran through the truck last night. 

 

Looks like I had ~6v at both the fuse and the connector with switch off. ~12.5v with switch on in all locations.

 

Bulbs passed a visual check, but failed a continuity check. Replaced bulbs and all is good.

 

Been driving for 30yrs now and have never had BOTH headlight bulbs fail at the same time before. Very odd.

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I ran a separate 4ft ground cable from the battery negative to the ground bolt by the brake booster. I was having issues with the truck just shutting off while driving or not starting after being parked, one headlight not coming on at start up but then randomly it would start working ... Since this ground wire install, none of those things happened.

I think its a great idea to just run an extra ground anyways.

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