rev counter

Hi John, I have moved your thread to the P6 electrics section, you may get a better response here.
Check the pins on the back of the tacho. IIRC one is a spade, other is a bullet - disconnect both and apply some Deoxit. Also do the connectors on the coil.
Deoxit is stuff that promotes conductivity where needed, see link. Not cheap, but I have had my pen for > 10 years. Apply it whenever I disconnect fuses, blade connectors etc. Also use on ground fittings.