Peter,
My apologies in advance, you are probably going to steam gently when you read this, but by far the easiest and surest way of knowing which fuse feeds what is by removing the fuses one by one and checking out what doesn’t work when that particular fuse is removed. To understand where I’m coming from put yourself in the position of the chap wiring up your car who will have been faced with a load of white wires and a load of green wires coming out of the harness at roughly the same point, also a load of brown and purple wires for the other fuse box. It matters not a jot to him which white wire goes where on the fuse box or indeed which green wire, all he’s got to do is get the whites and the greens to the same fuse box, ditto brown and purple, and hey presto it’ll all work. It would have taken him considerably longer to order them to a set pattern.
So, you see, not even Tony Crook himself necessarily knew which fuse position fed what, which is why it’s not in the handbook. I’m not very good on odds but across two fuse boxes aren’t the odds of your car not being the same as any other in the order of 2 x 4x3x2x1 : 1
When you’ve worked out what’s what write it down, laminate it and stick it up somewhere in the bay - it can save an awful lot of time on the side of the road!
Much easier on a 410, there are essentially only two main fuses and if the petrol gauge drops to zero and the indicators don’t work at the same time, well that’s one of them!
As for all the white wires. I’m only familiar with a 410s wiring but standard wiring practise (was) for white to be used for all circuits that are to be live when the ignition is on. There are at most two lucar terminals off the back of the ignition switch when it is in this position and I counted at least nine feeds on the 410 to all the individual things that need to be on, or available to be switched on, when the ignition is on. Some of these are fused, hence your four fuses, but a number are not (or were not, in those days), including the ballast relay, the tachometer and coil, the relay that switched power to the heated rear window (not the heated rear window itself), fuel pump and others, but my photocopy of the 410 wiring diagram gets a bit blurry at that point. Convention was that the fused feeds that were live when the ignition is on were green, but the unfused feeds were white. But with only one “spare” lucar on the back of the ignition switch the only obvious point to take all the unfused feeds to their various destinations is from the live or input side of the fuse box. There are plenty of lucar connectors at that point. Which accounts for all the white wires, only one will be “in”, the rest will be “out”. How are all the ins and outs connected? I’m pretty certain, but can’t actually swear to it, that there will be a strap between some or all of the “ins” within, ie on the back of, the fuse box.
I realise this doesn’t resolve your meltdown, but I hope it may provide some useful insights.
But as far as the meltdown is concerned my advice, for what it’s worth, based on Morris Minor experience, is to leave well alone if everything works. The insulation is still likely to be ok, but brittle, so fiddling with it is the worst thing you can do, and even if there is a short within it between white and white that really isn’t a problem. If there were a short to any other group of circuits there are likely to be all sorts of odd effects, which you don’t mention so presumably that’s ok too. The only other route out of it is a new wiring harness, which I would not fancy.
My regards
Roger
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