Robbie,
Yes you can. Probably. I managed with some scuffed fingers. Take off the trim on the left hand side of the driver’s side footwell (RHD, right?), and feel up around the back of the speedo and tach. You are trying to find a small metal box as in the picture, secured (and earthed) by the knerled nut holding the tach or speedo into the dash. It may also be necessary to take off the trim under the dash.
Of course, the one you have may be OK, but not connected or not earthed properly. The case needs to earthed (through the nut). It has two other connection as in the diagram. “B” goes to 12v, “I” is the 10 volts out to the instruments.
If John provides an electronic one in the same type of case it will go back exactly the same way.
good luck.
best regards, iain
