2007 310 Sundancer: Port motor...

[AshKat]

2007 310 Sundancer: Port motor will not start without depressing the "Emergency Start" Switch, but will not stay running once switch is released.  Could alternator and batteries coincidentally gone bad at the same time?  Any help appreciated. 

[GEORGE]

How about the battery switches, are they all on, or the main circuit breakers located around the engine or bulkhead open? I thought the emergency start interconnects all batteries so if you are turning off the emergency start switch it takes them (the batteries) back to the engine they support. You could have shorted cells/cell in a battery. Anyway, these are just a few things I would check out. Good Luck!

[AshKat]

Thanks. Battery switches are on, and I jumped th main circuit breaker to make sure it wasn't that. I would think the alternator would take over after the emergency start gets the port running, but it just dies when I let off the emergency start button. It seems like too much of a coincidence for the alternator and batteries to go bad at the same time, but I have a new alternator on the way and will test the batteries with a volt meter this weekend.

[fwebster]

Some Mercruiser engines have a fusible link at the starter main terminal. If it blows, you lose all power to that engine. Alternator and batteries will check good but with a blown fusible link, the port side is going to be dead. By using the emergency start switch you are providing power to the port engine from the STBD side and it will crank and run but as soon as you release the emergency start switch, the port side will die like cutting off the switch.

[AshKat]

That sounds exactly like my issue. I'll check it out. Thanks.

[AshKat]

I always hate reading these threads when the answer doesn't get posted. So here it goes. I checked voltage on both sides of the breaker and the fusible link, and all was good. Then I called my mechanic, who didn't have time to come by before he left the country on vacation, and he walked me though it. Checked the key switch and no voltage. Turns out the key switch gets current from the ECU on top of the motor. Near the ECU is a wire loom whip with a small fuse box at the end (4 mini fuses with one backup space in the middle). The 15amp fuse was blown causing power to the switch to be cut. Replaced it, and viola. My mechanic is Da Man!

[GEORGE]

Ashkat: I agree with your reasoning. I truly appreciate you providing, "and now for the rest of the story" closure. I am going to have a look at my wiring harnesses for the fuse box on top! Thanks!

[MedicRN]

Probably not. There is a little white-beige ceramic block a little bigger than a small box of stick matches typically mounted on the fire-wall-bulkhead of the engine compartment called a "balance resistor". The entire engine ignition electrical system runs through it to control electrical surges to the harness. Cabin Cruisers, being self contained off the community electrical grid are still predictable, easy, but considerably more complex than your car.
Due to weather-humidity extremes, typical on the water, this ceramic block may develop a hairline crack through it. The surge of the battery and coil is enough to jump the crack and start the engine. But the post start switch-over to the alternator is just enough of a break in the ignition circuit to kill the engine. Part? $40.00 , labor? $150.00 (1 hr.) You might think of adding a dedicated battery for starting one engine...then charging both.
Have a great season !

[Teko]

Locate the emergency start solenoid it has a fuse on it or as it has been said look for a fusible link at the alternator.