I have just bought a repair circuit board for my electical tacho in my '75, but it comes with no instructions on how to carry out the repair. Can anybody who has done this job help, please?

Once you remove the old board, the new one goes back in, in reverse. I removed mine a couple years ago. It's a all day job, as the board is mounted behind the tach itself. To get to mine, I removed the center console, then removed all the screws from the drivers side. If I remember right, I also had to lower the steering wheel, so that the driver's side console would come out enough to get to the Tach. I looked though some of my repair manuals, but didn't find anything on this, but if I come across anything, I'll send it to you. Also, I am moving this to the electrical section, as it fits in there.
Bill.