Brake lights keep blowing fuses

monkeh · Dec 13th, 2010, 20:30

My brake lights seem to keep blowing fuses all the time, theyre running on a 15a, but no matter what fuse value thats in there, 25, 30a etc... they dont seem to last that long, 10 minutes at least, Ive replaced the bulbs, I did have halfords QR in them, Ive isolated specific bulbs, but nothing.
I only realised that for the past week, Ive had no brakelights- the car hadnt been used much.

Is there a wiring diagram for the brakes?
Can it be the brakelight switch?

monkeh · Dec 13th, 2010, 22:07

After isolating the tailgate-Pulling the connector from inside the car, above headlining, its still blowing fuses, however, after the last pop, I got the sacrificial unfused ammeter out and the 2 21w5 bulbs are pulling 1.86A... Is this right?
Power = Current x Voltage
So 21W/12v = 1.75
2 x1.75 = 3.5Amps
Im measuring 1.86A
Wheres the rest going?
If the bulb failure circuit wasnt a swine, Id gut a spare unit and bypass it.
HELP!

Michael J · Dec 13th, 2010, 22:13

Quote:

Originally Posted by monkeh

... theyre running on a 15a, but no matter what fuse value thats in there, 25, 30a etc...

Please don't do that. It is a very bad idea to use over-rated fuses.

monkeh · Dec 13th, 2010, 22:29

Quote:

Originally Posted by Michael J

Please don't do that. It is a very bad idea to use over-rated fuses.

They didnt last long, It was only used a temporary fix, they were the only fuse I had left en route to Hellfrauds.

RealEstate · Dec 13th, 2010, 22:30

Sounds like you have a short somewhere.

How about this for a start?

Pull the brake light fuse and remove all the brake light bulbs. Then measure the resistance at the lamp sockets. Of course it should be infinite - open circuit. If not there's a short. Then measure it again with your foot on the pedal - should still be open circuit.

I've not checked the circuit diag, but believe that's correct.

gpl1968 · Dec 13th, 2010, 23:00

Here are the 1995 diagrams.
Ther may be differences on the later cars but I have yet to find diagrams for these.

CTCNetwork · Dec 13th, 2010, 23:12

Hi,

The most likely culprit, in my mind, will be the cable package that passes through from the body to the tailgate. The cables do, over time crack and/or split.

Another possible option would be the cable to the center HLBL as the cable passes through and near sharp edges of the inner tailgate.

Des. . .

monkeh · Dec 13th, 2010, 23:36

Quote:

Originally Posted by CTCNetwork

Hi,

The most likely culprit, in my mind, will be the cable package that passes through from the body to the tailgate. The cables do, over time crack and/or split.

Another possible option would be the cable to the center HLBL as the cable passes through and near sharp edges of the inner tailgate.

Des. . .

I had my eyes on that a few weeks ago, A bulb went for some unknown reason, but after a bit of wiggling ans swearing at it it came to life, Ive disconnected the wiring from the HLBL from inside the cab and attempt the continuity checks tomorrow in the light, the resistance from the live wire in the tailgate to the socket is 21r... maybe looking at that. But I still dont understand why Im getting a lower current reading from the ammeter.
Im also going to check the towbar wiring as well...
Sort one problem and another pops up...
*Sigh* The joys of motoring.

monkeh · Dec 13th, 2010, 23:38

Quote:

Originally Posted by gpl1968

Here are the 1995 diagrams.
Ther may be differences on the later cars but I have yet to find diagrams for these.

Perfect... Thanks... Mines a 1997 model. Im sure its similar.

monkeh · Dec 14th, 2010, 00:01

Quote:

Originally Posted by CTCNetwork

Another possible option would be the cable to the center HLBL as the cable passes through and near sharp edges of the inner tailgate.

You sir have earned yourself a beer...
This annoyed me- Ive just been out there to have another go... Im turning out like adamsky working on cars at midnight!
I checked the continuity to each end, but I didnt check the continuity to earth- Int. DEAD short... The cabin lights dimmed every time I tapped the brakes... There was a lot of power going there.
I inspected the cable, found the chafe about an inch in from the tailgate pillar. Its been dressed with insulation tape for a temporary measure and was bloody awkward to get at. Theres more blood than paint there now.
Thank you very much guys...
The wiring diagram is helpful for future.
I can only assume the fuse went pop after because it had been weakened by previous current.
It now sits at 3.85A. With all 3 lights connected. Its got a 10a fuse because Ive blown all my b****y 15A!

Dec 13th, 2010, 20:30	#1
monkeh Pain in the backside Last Online: Yesterday 21:15 Join Date: Mar 2007 Location: Newport	Brake lights keep blowing fuses My brake lights seem to keep blowing fuses all the time, theyre running on a 15a, but no matter what fuse value thats in there, 25, 30a etc... they dont seem to last that long, 10 minutes at least, Ive replaced the bulbs, I did have halfords QR in them, Ive isolated specific bulbs, but nothing. I only realised that for the past week, Ive had no brakelights- the car hadnt been used much. Is there a wiring diagram for the brakes? Can it be the brakelight switch? __________________ 'Designed by a computer, built by a robot, and driven by a f***ing nutter' '09 XC70 SE - 2" lift, D5 225bhp, poverty spec '18 V60 Twin Engine R Design - 290bhp

Dec 13th, 2010, 22:07	#2
monkeh Pain in the backside Last Online: Yesterday 21:15 Join Date: Mar 2007 Location: Newport	After isolating the tailgate-Pulling the connector from inside the car, above headlining, its still blowing fuses, however, after the last pop, I got the sacrificial unfused ammeter out and the 2 21w5 bulbs are pulling 1.86A... Is this right? Power = Current x Voltage So 21W/12v = 1.75 2 x1.75 = 3.5Amps Im measuring 1.86A Wheres the rest going? If the bulb failure circuit wasnt a swine, Id gut a spare unit and bypass it. HELP! __________________ 'Designed by a computer, built by a robot, and driven by a f***ing nutter' '09 XC70 SE - 2" lift, D5 225bhp, poverty spec '18 V60 Twin Engine R Design - 290bhp

Dec 13th, 2010, 23:12	#7
CTCNetwork Forum Support Team Join Date: Dec 2004 Location: Liège, Belgium View Photos By: CTCNetwork	Hi, The most likely culprit, in my mind, will be the cable package that passes through from the body to the tailgate. The cables do, over time crack and/or split. Another possible option would be the cable to the center HLBL as the cable passes through and near sharp edges of the inner tailgate. Des. . . __________________ Density:- Not just a measurement ~ It's a whole way of Life.! ! ! I drive a Volvo, Please Don't Get In My Way! OldVolvos4Ever He shows up. People die. He vanishes. People should not be afraid of their governments. "He'll deliver more justice in a weekend than 10 years of your Governments should be afraid of their people... "V" courts & tribunals. Just stay out of his way." "I plan to."

Dec 13th, 2010, 22:30	#5
RealEstate Master Member Last Online: Nov 4th, 2018 16:06 Join Date: Dec 2003 Location: Berkshire & N Wales View Photos By: RealEstate	Sounds like you have a short somewhere. How about this for a start? Pull the brake light fuse and remove all the brake light bulbs. Then measure the resistance at the lamp sockets. Of course it should be infinite - open circuit. If not there's a short. Then measure it again with your foot on the pedal - should still be open circuit. I've not checked the circuit diag, but believe that's correct.

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