2008 205 Sport, 5.0 carb mercruiser....

[RBJones]

2008 205 Sport, 5.0 carb mercruiser. This boat has run like a top for the four years I've owned it. But lately I've had an intermittent problem of a blown 15 amp ignition system fuse. I suspect the engine interrupt switch because it seems the times it's blown has been when I was shifting out of reverse or forward and the motor died. Tried to restart and motor wouldn 't fire. If I replace the fuse it fires up sometimes and runs fine for a few days. Other times it just blows the fuse again. I've checked the switch with multimeter and it checks out open and closed as working properly. But I wonder if it may be shorting out sometimes when the cam that's activated on the throttle arm presses against the switch? Seems to be a flimsy part in my estimation. Anyone else had similar symptoms? My only other suspicion is that it could be caused by a bad ignition switch. Anyone had an issue with a bad ignition shorting out?

Thanks for any info you may have.

[wingless]

It may be that high current battery connections have deteriorated contributing to this problem.

If fixing this problem yourself, my suggestion would be to start with turning off the on board battery charger, then removing and isolating every single wire from every single battery negative terminal.

Once the DC wiring is "safe", then disassemble / inspect / clean / reassemble / properly torque / seal every single high current connection. A liquid brush on insulation is a good method to protect those connections.

Note that if the connection has deteriorated, then that can cause a voltage drop / current increase that could be contributing to the fuse failure.

[RBJones]

Thank you Wingless. That makes sense. Could such a voltage drop cause the circuit breaker on the top of the engine to trip also? As part of the high voltage circuit, can I assume that includes the distributor and spark plug wires?

[wingless]

YW

Yes, bad high current connections, causing excessive voltage drops, could also affect the engine circuit breaker, because "constant" load power consumption, w/ less available voltage means higher current.

No, the high voltage wires are not part of this high current discussion.