Re: Beta Marine BD722 Tach kicks in after I enable extractor fan!
If/when anything electrical happens randomly, it is 99% of the time the connections, just like Brian said. You should go check them out, because otherwise all the discussion on this topic will not be able to help you. Good luck. Oh, while you're at it, draw a wiring diagram, might help you and us understand things better.
Stu Jackson, C34, 1986, M25 engine, Rocna 10 (22#)