1984 QV Dead Speedo and Rev counter

Well it looks like the dash is coming out. I've attached a piece of wire to the brown/black terminal on the (disconnected) socket going into the Digiplex, the other end to my multimeter. Then the brown/black wire at the (disconnected) tacho end and despite unplugging every socket l, I'm still getting continuity, and a visual search for the brown/black wire has drawn a blank. I've found the two sockets on the left, and can see the wire there, but cannot get at the plug to disconnect it, or to follow where it goes.
View attachment 3363503

 

I manged to get the dash off enough to access the harness and connectors. Every socket was unplugged and checked and all were good, with no signs of anything untoward anywhere. Tried the tacho again and nothing.
Next I ran a bypass wire from the connector on the left of the dash to the tacho and no change, but when I ran a bypass wire from the Digiplex to the connector it worked. I can only think that someone has damaged the wire somewhere on the harness running from the dash to the engine bay. I've had the rear seats out and checked as well as I can, but the harness is protected by a thick plastic cover - which looks fine.
Job for tomorrow is to run a wire alongside the harness and connect it to the Digiplex and dash connector. I'll snip and shrinkwrap the original brown/black wire.
Then it's back to the speedo...

 

Does anyone have a photo (or part number) of the rehostat that is on the PCB behind the odometer.? Mine is completely missing, having been bypassed somehow.
The power supply issue to the speed sensor is likely to be a blown capcacor on the board, hopefully just a few pounds to replace.

 

That's brilliant! Hopefully I can get these last few bits sorted and get it back on the road in the next couple of weeks