Thanks, that's what I'm planning to do - I've figured out that the reading I'm getting from the nut at the moment appears to be the car's energy drain (I got my decimal point in the wrong place before!). It changes depending on the electrical load - it goes up when I turn lights/heaters etc. on. I watched the rev counter needle whilst I was doing this and saw it go up a little each time I increased the load!
I've also taken a signal directly at the coil and grounded at the rocker cover - it appears to be okay there. The reading I take from U1 at the fusebox is the same as the one from the nut at the back of the rev counter, so the issue must be somewhere between the coil and the exit wire from the fusebox. If I was a betting man, I'd put my money on a short in the fusebox. I haven't been able to check the entry point into the fusebox, because it's behind a tangle of wires. May look into it tomorrow.
I think the previous clocks were busted too, as on those the needle didn't move at all, so hopefully once I find the wiring issue, the clocks should at least work.
I'm calling it a day for now, as I've had an utterly miserable day so far. I've found out that the door membrames are probably gone as the bottom of the door cards are damp, the driver's electric window stopped working (probably due to the membrames, as I heard a fizzing noise coming from the door before it packed in completely). I noticed the new clocks I got had some DIY on the oil warning light, and the previous owner had cut into the blue circuit board, cutting through the circuit paths, so I couldn't get it working properly. So I did a transplant of the new rev counter/MFA into the old unit, and managed to spill all the other dials and LEDs onto the floor. I put it all together again and put it into the car, only to find the LEDs aren't working (reminder to self: diodes only work one way!). So I stripped down again, sorted it out, and managed to snap the speedo cable connector trying to put the damn thing back on. I put the dash together again to find out one of the dash bulbs stopped working (luckily I now have plenty of spares
)
That's progress for you.
Rant over - I needed that
