Brake Light fuse keeps popping

My 91 XJS V12 convertible has started popping the brake light fuse, this fuse feeds the brake lights, turn signals and transmission kick down. I replace the fuse put on the signals everything works as it should, I got someone to press on the brake pedal while I looked at the lights all three light up with correct brightness OK, but sitting at the traffic lights with my foot on the brake after a few minutes I heard the fuse pop, then no turn signals and no brake lights, any ideas out there besides the XJS phantom ghost in operation! I did read a similar post but it had no replies.

I seem to recall i had this problem when i first got mine five years ago. I think one of my rear brake light sockets had corrosion, and was shorting the circuit when brakes applied. Somehow the bulb didn’t blow?

Gave the socket a good clean, and seemed to fix it.

Thanks, I will check that, the only thing is when I looked at them lighted they were all the same brightness, I did have a thought that they were the old original fuses but they blew in the middle and not at the connection, I put new fuses in we will see how it goes. It is going into the shop tomorrow for a new aluminium radiator install, don’t want to spend any more expensive shop repairs on this problem!

Just checked it again, sat there idling with my foot on the brake and after a minute or so the fuse blew, thinking of putting a 15 amp fuse in place of the 10 amp and see what that does, very weird, but it’s an XJS! That we all love!

Do NOT replace with a higher amperage fuse unless the one in place (that keeps blowing) is not the correct one, I would suggest that you check that first.

Agree, keep a 10 amp in place.

Since it happens when foot is on brake, obviously there is a short in the brake circuit.

It only takes a few minutes - I’d take off your tail lights, pop out the bulbs and check them (how old are they?), and then check the sockets for corrosion. Hopefully that’s all it is. If all looks good, then I’d check the wiring to those sockets.

Putting a higher fuse in place could heat up the wires more and cause them to melt.

And this isn’t an XJS problem. It’s an old car problem. 33 years is enough time for a bit of corrosion.

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take out the all the bulbs and put foot on the brake. Fuse doesn’t blow. Start adding bulbs, one at a time and check until fuse blows. Check out the last added for issue.
My 2 cents.


If you like the smell of burning insulation, a destroyed wiring harness, or potentially a vehicle fire, go ahead and use a larger fuse. Fuses are there for a reason. Find the problem and fix it.


Remove all light bulbs, apply the brake as you say, and wait to see if the fuse blows.

If the fuse blows, there could be a wire shorting out or worn and possibly arcing, blowing with longer term current from keeping the brake pedal pushed down.

If the fuse does not blow, replace one bulb only … I repeat, one ping only (Red October) … and hold the brake down.

If the fuse does not blow, repeat one lamp at a time until you find the one which blows the fuse.

You have then isolated the problem to one wire, socket, or something from that bulb back to the previous connection of that wire.

Well pretty silly of me thinking of putting in a higher rated fuse! car went to the shop today to have a new aluminium radiator put in, I told them to have a look at the brake light issue, but not to put too much time into something I think I could fix, being my wife’s 24/7 caregiver with only minimal help I really don’t have that much time to diagnose faults and repair the car, managed to put a horn button in my 87 V12 coupe with the new NRG steering wheel though, had to get a spacer to make room for it.

My mechanic put in the new aluminium radiator and found the problem with the brake light fuse popping, apparently it was something to do with the cruise control electronics, the cruise control mechanical bits have been removed from the car so he isolated the electronic part and the fuse stopped blowing. BUT when taking the car for a test drive a woman ran a stop sign at speed and he crashed into her! Hopefully it can be repaired and the insurance company won’t write it off, I love this car.

If the bulbs are removed, The circuit would be open. Nothing happens?

OTH, a short weould complete the circuit nd blow the fuse.

Another place to look. The brake light switch.
And the wires near that switch.