Chasing a Short Circuit Downstream of the Fuse Box on an E30 BMW 318i

The gauges in the instrument panel of my 1984 BMW 318i are, with the exception of the speedometer, all dead. I checked fuse #10 in the fuse box, and yep, this mighty 30 amp fuse was blown. That would explain the dead gauges.  I replaced the fuse and as soon as I turned the ignition key to “on” the fuse blew again.

So, the issue is a short-circuit downstream of the fuse.

I looked at the documentation, and it shows how the wiring from the fuse goes along three separate wires, two of them being green-and-white and attached to the instrument panel, and the third wire going … well, I haven’t as yet been able to figure that out.

This makes the instrument panel the prime suspect. I removed it, installed a fresh fuse, turned on the ignition key … and the fuse blew again.

So, now I can conclude that the issue is a short-circuit between the fuse and the third wire, wherever that goes, or in the wiring or connectors for the two green-and-white wires.  I was hoping for an easy fix, but … no such luck.

The bottom of the fuse box has always seemed intimidating to me, but tonight I dealt with it.  I disconnected the battery, and I took off the clear fuse box lid, and saw a Philips screw. I removed it.  I tried to lift the top of the fuse box, but it didn’t budge.  I removed the two relays close to the firewall, and found a second Philips screw, sort of diagonally opposite the first one. I removed it, and then I was able to lift the top part of the fuse box off. Yay!

Next to the inboard row of fuses, including the #10 fuse in which I’m so interested, was a set of four black plastic catches. I slipped these, and it loosened a piece of plastic whose purpose perplexed me, and aside from that it didn’t seem to make a difference.

So, I peered underneath and saw a couple of green-and-white wires, wound together and coming out of the area where fuse #10 would be.  Interestingly, although both wires were green-and-white, they had different styles so it was possible to tell them apart.  Clever, these BMW engineers.

I traced the wiring and saw the two green-and-white wires vanish into a massive wiring harness that exited the base of the fuse box.  I loosened an 8mm bolt at the front of the fuse box base, and was able to lift the base up enough to see the wiring harness go through a hole in the firewall.  I opened the driver door and peered underneath the dashboard area, and I could see the area where the wiring harness entered the passenger compartment.  I could even make out the green-and-white wires.  So, now I get to trace these, inside the car.

IMAG9289I put the fuse box components back the way they were, except that the black plastic piece didn’t fit as snugly as before. I hope that won’t cause problems.   I reconnected the battery, then started the car to make sure it would start and run. It did.  Yay!



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