Help!

[ian85]

Hi

Got my Exocet started up yesterday, but has a engine management light on. Plugged a diagnostic tool in today and the engine stopped and blow the engine management fuse 15a in the fuse box. Also there is 12v coming down the all black wire to diagnostic socket, which I am sure it shouldn't!. Any ideas or has anyone had this before

[sheffjohn]

What year is the donor wiring?

[jason82]

Check for a trapped wire, it sounds like a dead short. Check where the loom runs tight to the chassis etc in case of chaffing.

[ian85]

It's a 2003, I can't work out how I have 12v down the all black wire! It's pin 4 on the diagnostic socket

[jason82]

Black wires are earths. It sounds like a short. Do you have 12v down the black wire before the ignition is turned on or after ? This will help you to diagnose which circuits to look at. Once you know whether it's a permanent live or a switched live that is causing the issue, start pulling fuses until the fault goes away. This will tell you exactly which circuit(s) have the fault, then simply follow the wiring by hand until you find the fault. To be honest, once you have a positive feed going down an earth wire to the ecu, it may blow the computer. There are very sensative components in there.
There is no real fast way of trouble shooting, I am an electrician by trade (domestic & industrial, not an auto electrician, but the principles are the same). While doing your checks, also check that wires are terminated properly onto their correct locations.
It's up to you if you follow my advice, just trying to help.

[sheffjohn]

If you replace the fuse and remove diag tool, does it start run and behave as before?
I have zero idea how 12v on one of the shared earth's there even allowed your car to run to be honest.

[ian85]

Thanks guys for your help! I have now sorted the wiring fault. It has taken 4 hours of my life, but I found the problem a couple of hours ago and have sorted it!

After removing the tape around the wiring loom near the end bonnet diagnostic socket, I found two wires had rubbed through and touching each other!

What are the chances! Could believe it,pulled them apart and it started up and engine management light went out.