Having Electrical Problem Blowing Brake Light Fuse - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Desert Rat** · 01-13-2003, 07:58 PM

Electrical is not my area of expertise.Just recently my truck started popping the tail/brakelight fuse. and recently when i start to put the key in the ignition it sparks.anyhow upon putting a new fuse in it sparks and pops as soon as i put it in(yes with key and headlights off)did this with 4 fuses(correct amps)unhooked battery put one in,as soon as i hooked battery back up it blew again,so this morning in the dark,i used a bypass jumper wire(not something i care to do)and on the way to work about 2 miles it melted the thick gauge wire.any ideas,of where to look? i know everyone will say check your grounds,been there unless i over looked something?it was fine when i last parked it,but blew on its own while sitting,and theres power there when key and lights are off.Any help very much appreciated.

Gordo · 01-13-2003, 08:05 PM

Follow that melted wire, it may lead you to the cause. Doing that is what we call the "smoke test". You could also rig up a 10 Amp circut breaker in place of the fuse and trace the "warm" wire back to the problem.

**Desert Rat** · 01-13-2003, 08:14 PM

the wire it melted is the one i used to bypass the fuse i used roach clips and wire and hooked to each end,just so i didnt get pulled over on the way to work(not my way of doing it to fix)it was a get me by for the moment,thats the wire it melted,not one in the harness.

our64 · 01-13-2003, 08:19 PM

The wires to the brake light run along the frame and are easy to find. Follow them back from the brakelight switch. Its likely the insulation has rubbed off on the frame and the bare wire is shorting out

Vince M · 01-13-2003, 08:21 PM

Your tail light harness unplugs in a couple of spots..First try and disconnect the wiring harness for the tail lights at the firewall and put a new fuse in and see if it blows. If it does the problem is inside the cab. If it doesn't blow, plug in the harness at the firewall and disconnect it at the rear connector. It is mounted through one of the rear crossmembers. Keep trying this and it will get you close to the problem area.
I had problems with mine when i bought my truck. It turned out to be the wires at the back of the bed that go from one side to the other for the lights. Wires were old and the insulation had broken off in places and would ramdomly touch the frame.

Good luck

Gordo · 01-13-2003, 08:23 PM

Could be in the signal switch also, the brake light circut passes through the signal switch. Unplug the signal harness and see if the fuse ( or install a breaker for testing purposes) still pops.

**Desert Rat** · 01-14-2003, 05:00 PM

I had traced all wires everything ok,it was in the column,parts now replaced thank goodness i had a dimanteled tilt for parts!Was rebuilding guess it will get all new parts now for the next truck.Was frustrating until i found it,thanks for the tips.

01-13-2003, 07:58 PM	#1
Desert Rat Senior Member Join Date: Dec 1999 Location: Darrington, Washington Posts: 3,963	Having Electrical Problem Blowing Brake Light Fuse Electrical is not my area of expertise.Just recently my truck started popping the tail/brakelight fuse. and recently when i start to put the key in the ignition it sparks.anyhow upon putting a new fuse in it sparks and pops as soon as i put it in(yes with key and headlights off)did this with 4 fuses(correct amps)unhooked battery put one in,as soon as i hooked battery back up it blew again,so this morning in the dark,i used a bypass jumper wire(not something i care to do)and on the way to work about 2 miles it melted the thick gauge wire.any ideas,of where to look? i know everyone will say check your grounds,been there unless i over looked something?it was fine when i last parked it,but blew on its own while sitting,and theres power there when key and lights are off.Any help very much appreciated.

01-13-2003, 08:05 PM	#2
Gordo Registered User Join Date: Jan 2001 Location: Killingworth, CT. USA Posts: 3,378	Follow that melted wire, it may lead you to the cause. Doing that is what we call the "smoke test". You could also rig up a 10 Amp circut breaker in place of the fuse and trace the "warm" wire back to the problem. __________________ 1971 C10 swb stepside 350/700R4/3.73posi (retired as of 4/22/03) 1998 S10 short bed 2002 S10 Blazer 1942 Oldsmobile 1958 Massey Harris Pony 1951 Wife Killingworth, Connecticut May those who love us, love us, any of those who do not love us, may God turn their hearts. And if God is unable to turn their hearts, may he turn their ankles so we may know them by their limping. A man who works with his hands is a laborer; a man who works with his hands and his brain is a craftsman; but a man who works with his hands and his brain and his heart is an artist.

01-13-2003, 08:21 PM	#5
Vince M Senior Member Join Date: Apr 2000 Location: Orlando, FL Posts: 1,076	Your tail light harness unplugs in a couple of spots..First try and disconnect the wiring harness for the tail lights at the firewall and put a new fuse in and see if it blows. If it does the problem is inside the cab. If it doesn't blow, plug in the harness at the firewall and disconnect it at the rear connector. It is mounted through one of the rear crossmembers. Keep trying this and it will get you close to the problem area. I had problems with mine when i bought my truck. It turned out to be the wires at the back of the bed that go from one side to the other for the lights. Wires were old and the insulation had broken off in places and would ramdomly touch the frame. Good luck __________________ ............................................................ 68 Chevy CST SWB w/LS1, carb & 700r4. Golden Anniversary clone with a few improvements.

01-13-2003, 08:23 PM	#6
Gordo Registered User Join Date: Jan 2001 Location: Killingworth, CT. USA Posts: 3,378	Could be in the signal switch also, the brake light circut passes through the signal switch. Unplug the signal harness and see if the fuse ( or install a breaker for testing purposes) still pops. __________________ 1971 C10 swb stepside 350/700R4/3.73posi (retired as of 4/22/03) 1998 S10 short bed 2002 S10 Blazer 1942 Oldsmobile 1958 Massey Harris Pony 1951 Wife Killingworth, Connecticut May those who love us, love us, any of those who do not love us, may God turn their hearts. And if God is unable to turn their hearts, may he turn their ankles so we may know them by their limping. A man who works with his hands is a laborer; a man who works with his hands and his brain is a craftsman; but a man who works with his hands and his brain and his heart is an artist.

01-13-2003, 08:14 PM	#3
Desert Rat Senior Member Join Date: Dec 1999 Location: Darrington, Washington Posts: 3,963	the wire it melted is the one i used to bypass the fuse i used roach clips and wire and hooked to each end,just so i didnt get pulled over on the way to work(not my way of doing it to fix)it was a get me by for the moment,thats the wire it melted,not one in the harness.

01-13-2003, 08:19 PM	#4
our64 http://public.fotki.com/street Join Date: Nov 2002 Location: Winnipeg, Canada Posts: 169	The wires to the brake light run along the frame and are easy to find. Follow them back from the brakelight switch. Its likely the insulation has rubbed off on the frame and the bare wire is shorting out

01-14-2003, 05:00 PM	#7
Desert Rat Senior Member Join Date: Dec 1999 Location: Darrington, Washington Posts: 3,963	I had traced all wires everything ok,it was in the column,parts now replaced thank goodness i had a dimanteled tilt for parts!Was rebuilding guess it will get all new parts now for the next truck.Was frustrating until i found it,thanks for the tips.



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