[JL8Jeff]

I think it's either the ignition switch or the wiring from the switch to the (S)tart post on the solenoid. I connected a battery cable from the battery to the (S)tart post and it cranks over. When I turn the ignition switch, I see the voltage through the multimeter starts around 8-9 volts and builds to 12.5 but it doesn't engage the solenoid. When I let go of the key, I can hear a clunk which I think is the solenoid plunger dropping back. I'll try a new wire from the switch to the solenoid to see if that works, then maybe a relay to get full power from the battery. I tried a ground from the block to the boat hull, but that didn't make any difference. I tried another battery and got the same results.

Update: It's the yellow wire, I jumpered a new wire from the switch to the solenoid and it cranks over fine. I tried cleaning up the ends and the wire harness connection for the yellow wire and still no good. It lets power through but it's not clean enough to engage the solenoid.