Brake light woes...need help!
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Senior User
Joined: Jan 2011
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From: Dothan, Alabama
Brake light woes...need help!
I have 78 f150..It seems to keep blowing the brake light fuse..20 amp is what I just replaced it with and I replaced my left brake light because the dual filament was broken.. I press the brake or/turn on the hazard flashers and i can see a small arc...and the fuse I just replaced has blown again. I have read that its a bad ground?? Is that right?? If it is where do I need to start?! If it is a ground how do I know that its bad?
Hotshot
Joined: Apr 2009
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From: Stanley, VA
No, it's not a bad ground. You have a direct short somewhere in the system.
Where do you see the "small arc"? I'd start there, but the short can be anywhere in the brake light system. This includes the turn signal switch because the brake lights operate through the turn signal switch.
First, do a visual inspection of all the wiring related to the brake lights, starting at the fuse block, up under the dash to the brake light switch and turn signal, along the drivers side frame rail and the tail lights themselves and the harness that ties the two of them together.
Where do you see the "small arc"? I'd start there, but the short can be anywhere in the brake light system. This includes the turn signal switch because the brake lights operate through the turn signal switch.
First, do a visual inspection of all the wiring related to the brake lights, starting at the fuse block, up under the dash to the brake light switch and turn signal, along the drivers side frame rail and the tail lights themselves and the harness that ties the two of them together.
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Senior User
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From: Dothan, Alabama
The small arc was coming from the fuse itself... I did what you said...I started at the fuse block...nothing..worked myself all the way under the truck still couldn't find anything. I then unplugged the tail lights that from underneath the truck bumper at the harness. It no longer arced...so I am assuming that its from that plug to the taillights... Would that be a safe assumption?
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Senior User
Joined: Jan 2011
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From: Dothan, Alabama
ok I think I found it! It was the rubber boot of the harness itself...I could not find any other source...So I filled the rubber boot with dielectric grease and it no longer arcs! I guess it was a loose connection...Thanks for your help Mike!! 
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