Originally Posted by xs 400
....readings red oudboard positive 6v dc tickover up to 10v dc revving
green wire 3v ac tickover to 5v revving.
What strikes me as a little suspicious there is the AC readings are exactly half the DC readings.....
I remember the big discussion but no time to dig it out & read it again today. You do have a charging kit or similar, i.e a rectifier / regulator? The tacho counts alternator pulses, not voltage, and should be plummed in on the alternator side of the rect / reg. If your regulator is gubbed or has been wired wrongly (such that one half of the AC wave is being passed through & the other totally blocked) that might explain the funny DC voltage.
Try disconnecting the red (+) between the engine & battery & see what happens. (Keep the earth or there will be no return for the tach signal)