My head unit goes into "protect" mode, which I presume is caused by a short somewhere. Unfortunately, this fault only appears when the head unit is in place, which is making it very hard to troubleshoot. If I remove the head unit, it works fine, so I'm presuming the fault is caused when the wires are in close proximity. I've insulation tape everywhere, trying to minimise the possibilty of a short. I guess the other possibility is this is caused by excessive heat? Any ideas - this is driving me nuts.

What brand of stereo?

Only things I can thing of are trapped wires or over-heating...

It's a Kenwood, I've tried another headunit (JVC) which didn't have a protect mode but just cut out. I've the wires as neat as I can get them Thinking about it again, it probably isn't heat as it stays in protect mode even when cold. Maybe I'll just have to start from scratch and rewire everything

Ah I know the problem. Either a blown speaker, or one of your speaker cables is earthing out against the body.

Genius! Just checked, my rear left speaker isn't working ... I'll yank that cable out of the ISO block and see if that sorts it.

Matty, you're a fccuking genius - this seems to have sorted it . This has been one of those small problems that drives you up the wall, I've had the head unit out countless times - usually ripping my fingers up in the process. Now to sort the speaker out! Ta very much mate.

No probs buddy, I know how much this kind of fault can drive you insane.