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I'm currently neck deep in an electrical issue with my BMW 316i – I think I have a short circuit. I found the wires that are blowing my fuses, and it's bad. Like at least 5ft of 8 or more wires fused together behind my dashboard bad. I'm NOT looking forward to replacing said wires. I'm concerned that after I do replace said wires that whatever caused them to fuse together in the first place will just repeat its evil satan inspired process again. What could cause such a calamity?

I'm very, very, ignorant of engine/electrical systems and how they work, so please word your answers accordingly. Assume I'm electrically challenged, because compared to someone who knows what they're doing, I am.

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    Sounds like quite the short circuit. Did a bunch of fuses blow at once, or did one blow and then more follow later?
    – Parker
    Commented Jun 24, 2012 at 18:27
  • @Parker When I received the vehicle the electrical problem was already present. 2 of my fuses blow instantly whenever they are inserted into the box, and one blows whenever I press the brake (it powers my brake lights).
    – Ender
    Commented Jun 24, 2012 at 20:13

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I think the chain of events went something like this:

  1. Overload or short caused a fuse to blow.
  2. The root problem wasn't addressed and after replacing the fuse, it blew again, and again…
  3. Somebody got tired of replacing fuses and "upgraded" to a larger fuse.
  4. The larger fuse "solved" the problem (and helped to diagnose it as an overload, rather than a short – or at least not a "hard" short to ground).
  5. Over time the wires overheated enough that the insulation started to melt.
  6. It sounds like the problem still exists as fuses are still blowing.

Noticing that the fuse is the wrong size and going back to they correct fuse will stop the overheating – and will make the problem of blowing the fuse worse. If you are lucky the insulation has been damaged, but not so badly that there are new shorts in the damaged stretch of the harness.

Once you identify the oversized fuses, look it up in the owner's manual or service manual to see what devices the circuit(s) serve. That will get you started on sorting out the root cause of the fuses blowing.

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  • Correct. I found I had corroded wires resting in water underneath my driver seat, que your list:
    – Ender
    Commented Aug 20, 2016 at 20:42
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If you are not familiar with the electrical system I would get a referal to a good shop familiar with BMW's. They may have seen it before or at least recognize what caused it. This a case where it must be determined if your melted wires were the cause or the result of another problem. Just installing another harness may result in the same melted wires. The wires melted due to excessive current draw. Normally this should not happen because the fuse should open to protect the wires. It is possible that the wrong size fuse was installed allowing the wires to overheat.

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    when I received the vehicle the wrongs fuses WERE installed! I think you just saved me!
    – Ender
    Commented Jun 25, 2012 at 6:02
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Check to see how the wires are routed behind the dashboard. It's possible one (or more) rubs against something or goes through an ungrommetted hole. Eventually the rubbing wears through the insulation and the wire grounds out. And if you've got several fused together, you could have several spots where bare wire is exposed.

Good luck -- I hate having to work behind the dash!

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