When a motorcycle photo became a boat

[Lunchbag]

I was just settling in for another frustrating evening of troubleshooting a boat problem ...

What is the problem...?

The motor won't start or turn over when I turn the key.  It only makes a click.  However, when I short the terminals of the starter relay with a tool, the motor turns over and starts right up.

Coincidentally, I had identical symptoms on my '89 F150 just last week.  I put in a new starter solenoid and that fixed it.  But after I replaced the starter relay in the Yamaha F115, it did not fix it.  It had the exact same behavior as with the old relay.

I bench tested the old relay and it appeared good.  However that was not under load, so I can't really confirm it is good.  But since the new and old relays act identically, I think they are not likely the issue.

I cleaned up all wire terminals attached to the starter relay, but it didn't change anything.  The battery is new and I cleaned those wire terminals also, and like I said it starts up strong when I short the relay.

The only thing I can imagine is that somehow my 12V signal to the relay coil is weak and unable to close the relay properly to handle high starting current.  Just enough to make a click, but not to start.  Is that possible?

I think next I'll take a spare 12V battery and connect it directly to the small (coil) relay wires.  See if it starts up, and perhaps measure the voltage under load and no-load.

Then compare voltage under load and no-load while attempting a start from the console.  If voltage is low or voltage drop is severe, somehow trace the wires to find out where the drop occurs and repair it?  If all else fails, rewire with a good 12V supply?

Please let me know if you have other ideas...