My son, under my tutelage, has resurrected an old 115hp 6 cylinder blue band Merc.<br />We got it to run then looked at the ancillary electrics.<br />1. The tacho didn't work correctly initially but then we ran a secondary earth from the tacho to the general earth used for the gauges and it seemed to work fine. Now suddenly the tacho is stuck beyond the 6000 rpm peg and won't return to zero.<br />2. The charge coils seem to power the tacho at one input terminal of the rectifier. The tacho did not work when the lead was on one input terminal; I swapped it to the other and the tacho ran but not any more, as noted above. From checking battery charging rates after an engine run I'm not sure the coils are working. How do I check coil output? Presumably it will be a high-frequency ac signal on a voltmeter but what sort of voltage should I get from the input and outputs of the rectifier?<br />Any clues? Thanx in advance.
