Keep blowing brake light fuse!!!

WydRyd · 09-26-2004, 04:08 PM

Obviously a short circuit somewhere, but anyone got any tips where to start looking first?

This is p!ssin me off and scaring the crap outta me just thinking about the likelihood of someone ramming me up the A$$$$

ChrisL · 09-26-2004, 05:19 PM

One place to look is your engine light. My '86 had a small trouble light in the inside center of the engine cover. Turns out its on the same circuit as the brake lights. When that light was shorted out, it would blow the brake light circuit fuse. There is a disconnect for that light right under the oil filler neck.

Chris.

WydRyd · 09-26-2004, 08:44 PM

Thanks, will check that out

Tyson Schmidt · 09-26-2004, 08:52 PM

Check to make sure the wires to the back-up light switch are still plugged in at the side of the trans.

If the rubber boot is gone, they can fall out and touch ground. That will blow the fuse that they share with the brake lights.

filou · 09-28-2004, 09:25 AM

I have a question. Does the fuse blows during braking only ???
I had the same problem : everytime i was using the brake pedal, the fuse would blow. So i knew that the problem was AFTER the brake light switch at the brake pedal. Does your problem is the same ???
I found out that the switch was travelling too far and grounded the circuit everytime i braked.
That was a easy fix for me.
Good luck.
Filou.

Pipo · 01-04-2008, 06:07 PM

This thread is a bit old but I am having the same problem. My 86 911 is blowing the brake light fuse (#7) after a few tries of the pedal. All lights are working ok, until the fuse is blown. Any suggestions on where do I start checking? Thanks.

911pcars · 01-04-2008, 07:10 PM

Sometimes it helps to isolate the circuit.

Separate each harness connector in the engine compartment (rear corners) in turn and see if the fuse still blows. If not, it's in one of the disconnected harnesses leading to the light housing.

Remove the offending light housing and check continuity between source wire and ground for continuity. Visually inspect for worn insulation. Wiggle the harness while observing the ohmmeter.

Hope this helps,
Sherwood

pozee · 01-05-2008, 05:32 AM

Pipo,

+1 on what Sherwood suggests.

Do you have a 3rd brake light?

If the harnesses are tough to remove, remove all brake light bulbs. Then try and blow the fuse. If the wiring at your housings looks good and the fuse blows, it's probably the switch. If it does not blow, put one bulb back in and try to blow the fuse again. If it blows, then it's that particular housing. It's quite possible that you have a ground fault in the actual bulb holder that is causing the problem.

Barrpete · 01-05-2008, 05:52 AM

+1 on the third brake light. Had the same problem on my 86 & it turned out that the insulation had worn off the wire and it was shorting to the housing.

Pipo · 01-07-2008, 06:36 PM

You guys were correct. I dropped the third light and had my daughter pressed the brake pedal while I was watching the housing, smoke came out, fuse blew. Just like Barrpete said, insulation had worn. I wrapped it with some electrical tape, problem solved. Thank for the guidance.

GaryR · GaryR's Garage

Just to offer another twist to the brake light fuse problem, this time on a 78 SC. My car is a track car and the brake lights must work or it doesn't go on the track. I was down in W. Virginia last weekend and I was told my brake lights were out. Checked the fuse and immediately noticed two tings. First the fuse was obviously blown, second it wasn't the 16A (white) fuse that belongs in there, it was a red fuse that was at least a 30A (wide, thick band). My guess is the PO had problems in the past. Put a new 16A in and it worked for a 1/2 a run group and blew. From then on as soon as I turned the key on any fuse in there blew, up to a 25A I carry.

Time to look at the wiring diagram and current flow. Two wires exit the fuse. One powers the brake light circuit and the other the reverse lights. As the reverse lights are a waste on this car the wire was removed and guess what... that's where the short is. Put a 16A fuse in and all is well. IF I needed reverse lights I would bother checking them out at my leisure but I don't, and even a road car doesn't "need" them as compared to brake lights.

Just one more quick thing to check if you are w/o brake lights.