Keep blowing brake light fuses - The 1947 - Present Chevrolet & GMC Truck Message Board Network

sleepyboy · 09-06-2005, 07:22 PM

I keep blowing brake light fuses. When this happens, I lose brake lights, rear running lights, and the left turn signal (right works fine). All my grounds were reworked. Bulbs are correct. Fuse is a 20 amp. Any ideas? Is it safe to go a 25/30 amp fuse without needing a fire estinguisher?

67 SS · 09-06-2005, 07:37 PM

Check for bare wires in the wires to the back lights.

alf1096 · 09-06-2005, 10:36 PM

I would say the same thing there is a bare wire touching metal somewhere. be sure to look at the wires where the come close to the exhaust and where it passes throught metal and be sure and use rubber gromets

SCOTI · 09-06-2005, 10:58 PM

I had this prob occassionally w/my 68 after I first aquired it. I found that when someone did the exhast @ some point in time, they melted the insulation for the tail-light wires & they would sometimes ground out against the frame.

Check the wiring all along the frame, front to back, especially around the exhaust/muffler area.

mr402 · 09-07-2005, 11:45 PM

I also had the same issue when I first got my GMC. Drove me nuts because it was intermittent. I finally found the PO had cut off a harness for a trailer and there were a few bare wires just waving around. Took a long time to find because they were tucked up in the step bumper brackets. Good Luck and let us know what you find.

86swb · 09-08-2005, 02:07 PM

You do not want to put in a bigger fuse to sove the problem! I agree. You have a short somewhere. You will just have to follow the wires all the way back to the rear. This is what the fuses are for. So you do not have a fire. Hope you find the short.

**VetteVet** · 09-08-2005, 02:37 PM

Does this happen when you step on the brake pedal or when you use the left turn signal? The yellow wire that runs to the left brake light is powered by both those switches and the right light has a dark green wire that is common to both the brake light switch and the right turn signal. I suspect the yellow wire is shorted to ground.
If you have an ohmeter you can pull the bulb from the left turn signal and check the center terminals to ground and if one reads zero ohms then it is shorted. Here is a diagram.

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sleepyboy · 09-08-2005, 05:15 PM

Thanks guys, wire cut from old trailer harness grounding out. You guys are awesome..

SCOTI · 09-08-2005, 05:24 PM

Looks like mr402 gets the cookie . . .....

86swb · 09-08-2005, 05:32 PM

Glad to hear you found it. Good.

09-06-2005, 07:22 PM	#1
sleepyboy '69 Step Join Date: Mar 2005 Location: Marion, Texas Posts: 722	Keep blowing brake light fuses I keep blowing brake light fuses. When this happens, I lose brake lights, rear running lights, and the left turn signal (right works fine). All my grounds were reworked. Bulbs are correct. Fuse is a 20 amp. Any ideas? Is it safe to go a 25/30 amp fuse without needing a fire estinguisher?

09-06-2005, 10:58 PM	#4
SCOTI Registered User Join Date: Apr 2001 Location: DALLAS,TX Posts: 21,949	I had this prob occassionally w/my 68 after I first aquired it. I found that when someone did the exhast @ some point in time, they melted the insulation for the tail-light wires & they would sometimes ground out against the frame. Check the wiring all along the frame, front to back, especially around the exhaust/muffler area. __________________ 67SWB-B.B.RetroRod 64SWB-Recycle 89CCDually-Driver/Tow Truck 99CCSWB Driver All Fleetsides @rattlecankustoms in IG Building a small, high rpm engine with the perfect bore, stroke and rod ratio is very impressive. It's like a highly skilled Morrocan sword fighter with a Damascus Steel Scimitar..... *Cubic inches is like Indiana Jones with a cheap pistol.*

09-07-2005, 11:45 PM	#5
mr402 Registered User Join Date: Jan 2004 Location: Elmira, Oregon Posts: 449	I also had the same issue when I first got my GMC. Drove me nuts because it was intermittent. I finally found the PO had cut off a harness for a trailer and there were a few bare wires just waving around. Took a long time to find because they were tucked up in the step bumper brackets. Good Luck and let us know what you find. __________________ Enjoying life again. Time to get those big blocks rolling.

09-08-2005, 02:07 PM	#6
86swb Born a Chevy Man Join Date: Apr 2005 Location: Navarre, Florida Posts: 10,221	You do not want to put in a bigger fuse to sove the problem! I agree. You have a short somewhere. You will just have to follow the wires all the way back to the rear. This is what the fuses are for. So you do not have a fire. Hope you find the short. __________________ John or 86 (Viet Nam combat Vet-BIG RED ONE) '65-'66 1986 Chevy SWB Silverado 1984 Chevy Longbed Silverado New Kia Sportage (Wife's car and she loves it) CHEVY, American made w/pride! If you can read this, YOU NEED TO THANK A TEACHER! If you can read this in ENGLISH, PLEASE THANK A SOLDIER! GOD BLESS AMERICA AND BLESS OUR FIGHTING TROOPS

09-08-2005, 02:37 PM	#7
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,709	Does this happen when you step on the brake pedal or when you use the left turn signal? The yellow wire that runs to the left brake light is powered by both those switches and the right light has a dark green wire that is common to both the brake light switch and the right turn signal. I suspect the yellow wire is shorted to ground. If you have an ohmeter you can pull the bulb from the left turn signal and check the center terminals to ground and if one reads zero ohms then it is shorted. Here is a diagram. ----------------------------------------------------- __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative. Last edited by VetteVet; 08-30-2010 at 08:16 AM.

09-06-2005, 07:37 PM	#2
67 SS Registered User Join Date: Jun 2002 Location: NW ARKANSAS Posts: 258	Check for bare wires in the wires to the back lights.

09-06-2005, 10:36 PM	#3
alf1096 Registered User Join Date: Aug 2005 Location: Texas Posts: 124	I would say the same thing there is a bare wire touching metal somewhere. be sure to look at the wires where the come close to the exhaust and where it passes throught metal and be sure and use rubber gromets

09-08-2005, 05:15 PM	#8
sleepyboy '69 Step Join Date: Mar 2005 Location: Marion, Texas Posts: 722	Thanks guys, wire cut from old trailer harness grounding out. You guys are awesome..

09-08-2005, 05:24 PM	#9
SCOTI Registered User Join Date: Apr 2001 Location: DALLAS,TX Posts: 21,949	Looks like mr402 gets the cookie . . ..... __________________ 67SWB-B.B.RetroRod 64SWB-Recycle 89CCDually-Driver/Tow Truck 99CCSWB Driver All Fleetsides @rattlecankustoms in IG Building a small, high rpm engine with the perfect bore, stroke and rod ratio is very impressive. It's like a highly skilled Morrocan sword fighter with a Damascus Steel Scimitar..... *Cubic inches is like Indiana Jones with a cheap pistol.*

09-08-2005, 05:32 PM	#10
86swb Born a Chevy Man Join Date: Apr 2005 Location: Navarre, Florida Posts: 10,221	Glad to hear you found it. Good. __________________ John or 86 (Viet Nam combat Vet-BIG RED ONE) '65-'66 1986 Chevy SWB Silverado 1984 Chevy Longbed Silverado New Kia Sportage (Wife's car and she loves it) CHEVY, American made w/pride! If you can read this, YOU NEED TO THANK A TEACHER! If you can read this in ENGLISH, PLEASE THANK A SOLDIER! GOD BLESS AMERICA AND BLESS OUR FIGHTING TROOPS



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