Headlights still not working!
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Tuned
Joined: Jul 2014
Posts: 270
Likes: 3
From: Texas
Headlights still not working!
I pulled my 300 engine and painted the engine bay and then dropped in a 351w. I have an LMC heavy duty headlight harness installed along with all new grounds from the battery, to the engine, to the frame. The grounding strap from the intake to the hood is in good shape and the ones under the dash pad looked good. I swapped the dimmer for a known working one and went through 2 different headlight switches from the local parts store. The two new ones when install and turned on did nothing so I took those back. The original one shows no sign of melting or wear. When it is pulled to the first click all the dash lights and running lights work. When you pull it all the way out the dash and running lights go dim and flicker but no headlights come on. The switch makes like a clicking or scratching sound when in the headlight position but not when it is in the running light posistion. Im stumped and don't know what to do next. I need the truck for the 14th so time is ticking.
Thanks, John
Thanks, John
Senior User
Joined: Mar 2014
Posts: 354
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From: AZ
Just for fun, did you run a wire and ground directly to the headlight to be sure both did not blow? Ground to the post at the top of the bulb, then 12 volts to either side for low and high beam.
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Tuned
Joined: Jul 2014
Posts: 270
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From: Texas
I ran a jumper ground wire from the battery to the core support but that didn't help. Both lights worked before the swap and I even changed one for a known working one I had on my bench.
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Senior User
Joined: Mar 2014
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From: AZ
OK, I fell for you. I have run into some weird wiring in the past, but eventually figured them out. Since you changed the wiring harness, I started to worry. There is really nothing to is. Power, ground and switch. How about getting some power to the plug at the switch. If lights come on it is switch, if not, wiring issue. Then continuity test is needed for all lines.
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Joined: Nov 2007
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From: Denver Metro Area, CO
If the built-in circuit breaker is constantly tripping, this means you most likely have a dead short to ground somewhere.
Did you install this LMC harness when you changed engines and the problem then began? If so, that implies something is wrong in the wiring of that harness...
Did you install this LMC harness when you changed engines and the problem then began? If so, that implies something is wrong in the wiring of that harness...
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Tuned
Joined: Jul 2014
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From: Texas
The headlight harness is kind of a thing of its own. It has 3 connectors on it, 2 for the headlights and one male to plug into the old headlight plug. It just bypasses from all the energy running through the switch. Its hard to explain with my lack of electricity and wiring knowledge. Its in the lmc website of you want to take a look. I must be getting power at the switch because the dash lights And parking lights come on right?
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Joined: Nov 2007
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From: Denver Metro Area, CO
Sounds to me like there is too much of a ground someplace where there shouldn't be. Use your ohm meter to see if you have continuity between any of the headlight wires and ground; if you find a wire that shows such continuity, you found a wire with a problem somewhere.
The act of painting (or changing an engine) might have caused some insulation to be scraped or chaffed and a wire shorted to ground somewhere.
The act of painting (or changing an engine) might have caused some insulation to be scraped or chaffed and a wire shorted to ground somewhere.
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Tuned
Joined: Jul 2014
Posts: 270
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From: Texas
Okay guys I fixed it. Turns out since one of the old pig tails for the headlights isn't used because of the new harness, it sat to the side. I geuss bouncing around caused the plastic plug connector divider fell off causing the ground and positives to touch. Who would have known!
Thanks, John
Thanks, John
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From: Sheffield, AL
Last edited by ctubutis; Feb 11, 2015 at 09:37 AM. Reason: fix quote
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