Eletrical Mayhem, Wizard needed

So to start with it's an old I/O a 89 5.0L [Ford] with an OMC Cobra leg.
The problem began this spring.When I started the boat cold everything worked fine but after it had run for a while and I restarted it the starter would continue engaging after the moter fired up.I would kill it, try over [happens 3 out of 5 times] and then continue on.
The boat has a remote starter selinoid that was original that I thought was the problem.I replaced this then started several times at home no problem [not really representing true running temp]
Today I took it out on the water again.Once again fired up fine cold and on the first restart.Second restart the starter ran on again once,killed it,restarted no problem.
We are now 10 miles down the lake in the middle of nowhere all by ourselves.The third restart the starter runs on.I turn the ignition off, still running [starter and moter].I then turn off the battery Perko switch and kill it.We now try disconecting the ignition and turning battery on,still turning over wildly.
We disconect the starter lead, turn on the battery, and touch the lead to the terminal and the boat fires up with the ignition turned off.We cruise the 10 miles back with no issues, normal engine and electrical power and all instruments working.
When we get back and I go to turn the battery off the engine keeps running with the electrical power on the guage varying wildly.I had to pull the lead off the distributor to kill the engine.

Help!!!

you don't need a wizard, you need an exorcist.

sounds like the started soleniod on the starter has corrosion inside and when it heats up it binds up and will not release

If you turned the Perko switch to 'Off' while the engine was running you may have damaged the alternator. I've heard that this will send a surge back to your alternator and toast it. Maybe this is why your electrical guage is wildly fluctuating.

So I've worked my way from the ignition all the way back to the starter selinoid disconecting conections looking for shorts.I continue to have ignition power [when the connections are all together back to the gauges] and constant power to the starter even when I'm disconected right back to the selinoid.
So all that's left is the battery to the Perko to the starter selinoid.From here it's putting power out always.Sounds like the selinoid but that's what I just replaced without a change in symptom's [though now it's way worse]
Any ideas?

New boat! j\k

So it's the starter selenoid.I isolated it down to just the battery to the selenoid to the starter.There was still power going to the starter.When I put on my old selenoid [which wasn't working as bad] there is no more current going to the starter.
My question now is, what's making the selenoid crap out?I've looked over the grounds on it and all my wiring looks good [I can't find any bare wire for shorts].The wiring looks in pretty good shape in general [for a 16yr old boat]
Any thought's?