Brake Light Problem/no back up lights
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Freshman User
Joined: Jan 2009
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Brake Light Problem/no back up lights
I just got done redoing my 78 F250 entirely. I have it back together now and have no brake lights. The turn signals work and parking but no brake. I have 12 volts to the brake switch but as soon as i activate the switch or put a jumper wire in it, i loose the 12 volts. Any help would be grateful. Another issue i am having is the back up lights don't work so i'm not sure what that might be, haven't had a chance to dig in to that problem yet.
Senior User
Joined: Nov 2008
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Or upstream. I do work on a lot of electrical industrial equipment and you can get a false voltage reading. As soon as you put a load you loose the voltage that was shown on the meter. Very annoying and tough to diagnose if your not familiar. So just a word of advise you can take it for what its worth, don't overlook the upstream portion of the circuit.
Cross-Country
Joined: Mar 2008
Posts: 97
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From: KS
This may sound like a stupid question, but where are you sticking the negative (black) lead at for the ground? If you are using the opposite side of the switch your meter will read 0 volts when the switch is closed.
Now if you have the lead on a separate ground and you lose voltage when the switch is closed then you probably have a bad/poor connection (ie. corrosion, wire insulation under the terminal crimp, loose connection, bad wire, ect.) somewhere upstream acting as a load.
Hope this helps.
Now if you have the lead on a separate ground and you lose voltage when the switch is closed then you probably have a bad/poor connection (ie. corrosion, wire insulation under the terminal crimp, loose connection, bad wire, ect.) somewhere upstream acting as a load.
Hope this helps.
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Freshman User
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Yeah electrical is fun. And i'm not an idiot, i using the cab as a ground for the lead on my tester. I won't be able to work on it till later this week, but i had a thought today to take a jumper wire and throw 12 volts from a constant supply that i know is good to the switch and see if the lights work then, and in might thoughts that would eliminate whether it would be on the source side or load side of the wiring. Is my thinking correct.
Posting Guru
Joined: Aug 2008
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well what you could do and might be easier is take a test light and see if your light works , and then just follow the wire from the switch to the light you'll see the short soon enough but my guess is you sat the bed down on it
Posting Guru
Joined: Nov 2007
Posts: 1,305
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From: Montgomery, IL
And i'm not an idiot,...
Sounds like you have pinched or nicked a wire and it is causing a short. Check your grounds too. One loose ground can drive you nuts!
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Freshman User
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well one thing i didn't tell everybody was i put a flat bed on it and ran all the wiring after the body and bed were on the frame so that is kind of why was wondering if it could be something before the switch
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I had crazy bad electrical problems. I went through everything I could in my wiring. One minute blinkers worked great...then no brake lights...get my brake lights working...then Id have no driving lights. I ended up pulling my fuse box out ond taking a dremel tool and cleaning every terminal on there, front and back. Now everything works great! If you dont have a new fuse box check that. Hope you find whatever it is!
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