Stop light fuse keeps blowing

[Willybolly17]

Hi

Help please!!!

I have a problem that is driving me mad.

Every time I put the brake on the 10amp fuse on my L reg Defender 110 blows with a bright flash.

The indicator and fuel gauge are on the same fuse but these appear to work until I step on the brake.

I have used a multimeter (disconnected the earth terminal of the battery and connected the other terminal of the multimeter to the body work) and appear to have a short circuit (little or no resistance) on both the spade with 2 wires near the brake actuator (green and purple wires) and the two brake light connectors at the back of the vehicle with the lead to the lights disconnected and the fuse disconnected. Also when I connect the multimeter to either side of the fuse plug I also get a short circuit.

Am I doing something really stupid as I cannot believe that I have a short circuit on both sides of the fuse suddenly appear?

Having looked at the back of the fuse box - two green and purple wires go into the fuse box but a white wire seems to come out!

There are also green and purple wires at the back to the lights (brake and side lights) but on one side these go into a 4 way socket with a red wire and three green and purple - I may be a little confused here as there is a real spaghetti arrangement of wires some of which have empty connectors.

Can any one suggest where I should be looking for my short circuit?

[TerryS]

I don't know what year L is,(early to mid '90s ?) but that shouldn't matter as they are all pretty much the same.
You pretty much confused me as to how you're going about diagnosing the problem, so let me tell you what I would do given the same symptoms.
Obviously, blowing a fuse quickly is a pretty good indications there's a short in the brake hot line somewhere. Start by pulling the plug that joins the chassis harness to the main harness. It's on the right side of the truck, just under your pedal boxes, where the chassis harness runs down and into the right side frame rail. Now, turn on the key and step on the brake. I'm guessing the fuse didn't blow, so the short is in the chassis harness, and likely at the back of thetruck where it goes up into the right rear of the cabin.
The brake hot line ( green with red tracer, I think) goes into a spliiter and out to the right tail lamp assembly, and also into a short harness that takes all the light wires over to the left side (another likely spot for the short). You can take your multimeter, on the Rx1 scale, pull the two brake light bulbs, and look from the brake light socket forward.
The white wire at your fuse box is the switched hot, and that's going INTO the fuses.
The only other line to check, if the fuse still blows after pulling the chassis harness to the main harness plug, is the line out of the brake switch on top of the brake pedal box, to the harness plug. That's pretty unlikely.

[Willybolly17]

Hi

Thank you for your prompt response.

I had not realised that it was a site based in the States. L in UK means that it was registered in 1994.

I will try what you suggest and report back

[Willybolly17]

Hi

The harness to the back was the problem. The plug was in the engine compartment. From there the line runs into a box section and then out of the box section at the rear. The problem was as the harness came out of the box section - vibration had worn the harness covering and exposed the wires - it was not obvious but it must have worn through the stop wire covering - on moving the harness away there was no short circuit.

Thank you for your help.

[khooper]

I would think since you keep blowing fuses that you are shorting out somewhere. You need to inspect as much wiring as you can. Unfortunately it will take alot of time tracing some wires but replacing the fuses again is not going to help. Maybe a voltage regulator? Or the main battery cables? I hate electrical issues.
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[TerryS]

Originally Posted by khooper

I would think since you keep blowing fuses that you are shorting out somewhere. You need to inspect as much wiring as you can. Unfortunately it will take alot of time tracing some wires but replacing the fuses again is not going to help. Maybe a voltage regulator? Or the main battery cables? I hate electrical issues.
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