boggling taillights
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Joined: Oct 2003
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boggling taillights
having a problem with my 78 f150 tailights staying on. when my headlight switch is off, i have brakelights. but turn it on and poof.....no lights. i have played with the wiring harness to the rear lights and gotten them on, but as soon as i would touch the brake pedal, it killed everything. so i played with the lights, got them on, and disconnected my brake switch. something else killed my lights. could this problem be related to the turn signal switch? if not, what could it be? front lights are all working properly.
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Joined: Jan 2001
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From: Virginia
A bad ground in the back. This could be caused by the brass part of the bulb not making good contact to the socket, or the socket not properly grounded, or the ground wire is corroded where it connects. If the ground wire connects to the bed, the whole bed may not be properly grounded to the frame.
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flashers
something else to add to the mix here. bad ground has been ruled out b/c my rear side markers both work properly. but last night i was looking at the rear lights and i noticed that with my headlight switch off, my rear side markers and liscense plate lights also blink when the emergency flashers are on. is this supposed to happen 
? i have a turn signal switch coming later this week to see if that fixes these problems, but if it doesnt ill start looking for crossed wiring. can anyone tell me where to start looking for some crossed wires? everything at the quick connect in rear is spliced, but it appears to be correct.
? i have a turn signal switch coming later this week to see if that fixes these problems, but if it doesnt ill start looking for crossed wiring. can anyone tell me where to start looking for some crossed wires? everything at the quick connect in rear is spliced, but it appears to be correct.
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Joined: Jan 2001
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From: Virginia
bad ground has been ruled out b/c my rear side markers both work properly.
In your case the brake lights are finding a return path through the marker lights. But when you turn the marker lights on, it can't use this circuit anymore for the ground, so it cuts off.
As I said in the other post, the circuits are tied together at the bulb itself. The most common problem is the brass part of the bulb is not making good contact to the tang on the side of the plastic socket. I have also had the sockets go mysteriously bad, where no matter how much I cleaned the contacts, I could not get a good ground from the black wire to the brass part of the bulb.
