Very strange electrical problem plaguing the ol' crate

[The Goodz]

Hello all, isn't it great that I haven't posted on here in ages, and when I finally do, it's because there's something wrong with the bloody car? Lovely.

Anyways, just been out to glenmaggie for the weekend, and while I'm out there, we decide to go for a drive. We take off and all of a sudden all the electrics are going spastic, both volt guages (for the triple battery system) start clicking around at 10 volts, so obviously it was a short circuit. Open the boot and theres smoke around battery no. 2. It stopped when I switched the engine off, obviously because the battery isolator solenoid saw that the main battery wasn't getting charge, so it separates them. There location of the short was not clear, so I disconnected the whole triple battery setup and figured i'd fix it later. So off we go and when we go to leave from our destination, the engine starts missing and backfiring really bad, the tacho starts jumping up and down quite wildly (although the engine revs aren't moving so much, the wolf is showing the revs to be consistent and closer to 1000-2000 rpm), and also the fuel flap ajar light starts flashing. So I go back to the boot, and found that the plastic sheath around the connector of earth cable for batteries 2 and 3 was a little melted, so a pull the cable and it comes right away from the body, the connector itself had broken off somehow and must've been touching the body back and forth, creating sparks and god knows what. I pull it away, and there is absolutely no difference. It still plays up. At this stage I've disconnected the whole triple battery setup, the solenoid is disconnected, everything.

Now the wierd starts.

A few anomalies have appeared. The volt guage for the main battery (which is connected straight to main battery) reads around 13-13.5V. Normally sits at around 14V. The wolf is telling me the voltage is 14.1V, same as always.

This backfiring and carrying on and losing power thing is intermittant, it'll be alright for a few minutes, then come back on. But what I noticed is that it seems to happen after or while I press the brake pedal. Usually after releasing the brake pedal. And if it starts carrying on while I'm driving, a tap of the brake pedal seems to make it come good, at least for a little while, although the brake pedal seems to cause it a lot of the time. Sometimes while I pull up to a set of lights with the foot on the brake, the tacho will read 0 revs, but when I lift my foot off the pedal, it comes on again. This only happens some of the time. Also, if the tacho dies while pressing the brake pedal, if I indicate the tacho jumps up with the clicking of the indicator.

I have had a look round the engine bay and can't see any obvious shorts, the battery terminals are tight, and I'm certain it's not my mass of wiring that many of you have seen, because a lot of it isn't even being used. I've looked under the dash above the pedals and can't see anything obvious there either. I'm thinking it could be something to do with the brake pedal switch, as the brake pedal is definitely playing a part here.

Any ideas?

Thanks guys

Alex