Thread: Electrical short

Originally Posted by vnx205

Rave says that fuse 15 is for the LH parking light and the trailer pickup. On my Defender, it protects the LH parking light and the number plate light. Is that normal?

My most basic question is, am I right in thinking that if I have the switch off, leave the fuse out and remove the front parking bulb there should be no connection between the number plate power wire and earth?

Fuse 15 does the LH Tail light as well, so you'll have to pull that bulb too. Yes, the licence plate light is normally on this circuit. One other thing to check; this circuit provides the illumination signal to the stereo - if it has been butchered that might be your problem.

You're lucky it isn't fuse 16 - that does much more!

I still haven't found where the problem is.

I got all excited when you mentioned the illumination for the stereo because that light stopped working some time ago. However, I haven't found anything there yet.

I notice that my rear tail light is connected to fuse 16. I'm guessing that has something to do with the way the trailer wires were joined to the harness. I have removed the tape that was around the soldered connections there and can't see anything amiss.

Whatever was done to add the trailer connections has worked perfectly for the eight years I have had the vehicle and probably for the eight years before that.

With the radio disconnected and the front LH bulb (and the rear LH bulb) removed and the number plate light disconnected, a bulb replacing the fuse lights up when I turn on the parking lights confirming what my multimeter is telling me.

I would continue to investigate that tail light - by rights it should be on fuse 15... The wires that would've connected it to the fuse 15 circuit must be tucked in there somewhere and might be your fault.

Other than that, I think you've exhausted all of the easy solutions

Being a trayback, all of the wiring back there would've been done by whoever put the tray on, meaning I can't offer much more help than telling you how the wiring is on a station wagon is. My suspicions will always be the bits that aren't factory, because lots of people have soldering irons but very few understand electricity.

First suspect and guilty 95% of the time is the trailer socket - usually installed by the apprentice with a roll of electrical tape, solder and a cigarette lighter; although the last two are optional.

Second suspect is the rear light wiring, as the person who installed the tray is an unknown.

Third suspect is the stereo if non-standard, same reason.

The standard wiring very rarely goes wrong in a 300tdi. I've never heard of a short inside the chassis rails either although I'm sure it has happened - probably due to the aforementioned apprentice reefing on it so he can access it with his cigarette lighter.

Good luck.

That is the same logic that I have been following. The stereo seems to be the original standard one.

There are a lot of wires around the back, all neatly wrapped and encased in concertina tubing.

It looks like being a long search.

I have stopped it blowing the fuse (ie the standard fuse, not a lump of foil or a nail), but I am not as happy as I should be.

In spite of our low opinion of the standard of electrical work done by some apprentices or work experience kids, the wiring at the back and for the trailer connection is pretty professional, neat and tidy (apart from the LH tail light being connected to the same wire as the RH tail light.

So why am I not delighted with the outcome?

I decided to ensure that the fault was towards the back of the vehicle rather than the front LH side light. I unplugged the connector on the bottom of the firewall in the engine bay that takes the power to the back via the inside of the chassis. My test bulb in the fuse socket went out, so I knew I didn't need to look around the front.

Working on the assumption that the most likely place for the insulation to be damaged is where the wires pass through holes in panels, I looked at where they disappeared into the chassis. They are protected with a huge, soft grommet, but I pulled them out a bit just to check.

There was no sign of damage in the first few centimetres, but moving the harness at that point stopped it shorting. All the harness that is visible looks in very good condition and I can't reproduce the short by wiggle or pushing the wires.

All of that makes me think the problem may have been inside the chassis. However I can't be sure because I didn't actually find the location of the problem. The best I can hope for is that the harness inside the chassis is sitting differently. It may have been touching the outer wall of the chassis and it is now pulled back a bit off that wall.

As I said, I haven't been able to recreate the short by moving the wires. Maybe driving the vehicle another 220,000 km won't reproduce it either.