71 F250 lighting problem
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71 F250 lighting problem
Picked up an old F250 that had been rewired by the previous owner.If I can get it working properly I will put it to use pulling a goose neck stock trailer. It really is a pretty nice truck. Any way I could use you folks help.
With key off - push the brake pedal and it lights both back high elements dimly. If you turn signal the left it dims the left and lights both elements on the right side. If you signal right it does the opposite.
With key on - left or right turn signal blinks both back lights at the same time fairly quickly. If you pull on the marker lights the left blinks slowly and the right just stays put on the high elements. If you put on the brakes in this configuration the back lights go out.
All the lights on the front of the truck are working fine the whole time.
I have replaced the light switch and new wiring from the fire wall to the back. Prior to those 2 items I had 1 left back light that worked so I'm making head way but need help. Thanks in advance.
With key off - push the brake pedal and it lights both back high elements dimly. If you turn signal the left it dims the left and lights both elements on the right side. If you signal right it does the opposite.
With key on - left or right turn signal blinks both back lights at the same time fairly quickly. If you pull on the marker lights the left blinks slowly and the right just stays put on the high elements. If you put on the brakes in this configuration the back lights go out.
All the lights on the front of the truck are working fine the whole time.
I have replaced the light switch and new wiring from the fire wall to the back. Prior to those 2 items I had 1 left back light that worked so I'm making head way but need help. Thanks in advance.
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Joined: Jan 2001
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From: Virginia
Check the tabs in the sockets that ground the outside of the bulbs, and clean the outside of the bulbs. Then like Gene Stoner said, check the ground to the bulb. The later models have a plastic socket with a seperate ground wire, but you may have a metal socket, which has to make a good connection to the sheetmetal, and then the sheetmetal has to make a good connection to the frame. Don't be afraid to run a ground wire from the bed to the frame. I fixed one of my old trucks like this.
Post Fiend
Joined: Apr 2002
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From: Central Kali
It kind of sounds like you have a couple of wires shorted together. That always gives weird symptoms. 
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Posting Guru
Joined: Aug 2002
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From: Minneapolis, MN
Try touching the base of the rear bulbs when the problem is occurring with a test light probe with the probe connected to a known good ground. Use the negative battery terminal with a jumper to get enough length if necessary. It still sounds like a weak ground.
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Found the problems, shorted at firewall above plug (the black wire and the bed has a difference in ground potential from the chassis. Fixed the short then ran a wire from the ground the battery attaches, to the separate tail light bulb housings. Now it works.