[Nitrox]

I have a Mariner 150 Magnum III 91 / 92 vintage. On the whole the engine has been very reliable but of late we have broken down at sea twice. Once with Divers in the water and 12 miles off, very scary !For some reason the engine just cuts out after period of running, (this just maybe a stall related to the time spent with engine on idle while divers are in water - not main concern). Problem is just lately then engine has not always restarted - issue.We have checked just about everything and replaced the wiring harness which was defective (short when can in contact with water). But lately we have noticed that the battery charging circuit / rectifier may not be working leading to a flat battery. Assumption engine runs on battery for electrical power which decays battery to point where engine fails or unable to start engine after a stall ??)Our instruments are showing 12.4 volts whether engine is running or not ????? This does not appear right to me. I would expect the voltage to be higher voltage output when engine is running and charging battery i.e. 13.5+ V.Question: How can we check the output of the rectifier ? Or check whether the rectifier is working or not ? Is their any values to check ? All ideas welcome. Thanks

[bhile]

You already checked it. But to be sure, put a volt meter or multimeter directly on your battery and check voltages running and not running. It should be higher with motor running. If you indeed had a shorted wiring harness, there is a 99% chance your rectier is shot.

[ronmold]

If you have a meter put it on the AC range and check the yellow wires on the rectifier with the motor running. At high idle you should see 13 to 15 volts. If volts are low try removing one of the yellow wires from the rectifier lugs and test them. If you have lots of AC voltage but low DC when rec. is hooked up it is your rectifier.

[Nitrox]

Gents, Many Thanks for your responses they are both very useful. The point ref the defective harness may indicate the cause of the problem particularly as the harness fault was found to be defective insulation on the harness running through the hull. We found when the harness came into contact with water in the bilge it cause the starting electrics to short out. Thus it is feasible that running like this make have wrecked the rectifier. The test information is very useful which I will try this weekend but it looks like a new recifier maybe required.Again thanks for your collective help !!!