Hi all! I have had this problem for about 18 months (my last post on the subject was Dec-11) and have not got any where close to resolving it! I does bother me so I thought I will have another go!
I have a Beta Marine 20Hp Model BD722 (<400 hours) installed with a 5+1 way switch panel as you can see here:
The tach appears dead until I operate one of the switches on the panel!Switch one which is an extractor fan located behind the engine and will kick the tach to live. Based on the sound I think it is then pretty accurate for around 3000 revs during cruising .
Terminals and wiring all ok.
Battery light on ignition lights up and switches off after ignition.
Charger seems to be working as I dont connect to shore supply unless nececssary.
Recently changed fan belt and tension looks ok - same problem!