Starter/Engine

First I need to know if its a Ford without a solenoid in the starter or a GM with a solenoid as part of the starter. Its not hard to troubleshoot, all you need is a test light and maybe a couple wrenches for disconnecting some wires.

Purchase a small 12volt test light at any auto parts store. Disconect the small wire to the starter solenoid that comes from the ignition switch. I would like to tell you which wire it is but my boat is covered and we're still experienceng the affects of hurricane Katrina. Once you remove the wire take the 12volt test light and hook it to the wire and to ground. Cycle the ignition switch through the start position several times, the light should go on and off. If the light stays the problem is in the ignition switch, if it goes on and off when you cycle the switch its good.
Next: If you determine that the switch is good I would then check the relay (solenoid).
You can also follow the same proceedure with the starter side of the relay. At the relay remove the cable going to the starter, connect your test light to the relay terminal and and the other end to ground and then cylce the ignition switch. The light should cycle on and off. If it stays on, just for the heck of it disconnect the small switch wire again. If it still remains lit then its the relay sticking, if it goes out its back to the switch. If it does cycle on and off with the ign switch you either don't have a problem or its intermittent and you'll need to do this proceedure when it occurs.
Good Luck

Hey JAG459 you are right on. You saved me alot of typing. Your method is perfect. The only other possibility that could happen is you could have a bad solenoid even though it tests ok with a test light. This is due to the fact that with the starter connected, the solenoid could weld the contacts together and stick due to the high current draw of the starter versus the test light.

We had the same problem this spring with our '86 Ski Nautique 2001. The old solenoid was going out and purchased a new one. The second time we started the boat, the solenoid stuck. I had to disconnect the cable from the battery, but not before the battery ran down (no tools in boat).

Returned it as defective. The replacement stuck about a week later. My brother-in-law (auto mechanic & '76 Ski Nautique owner) hit it with a wood oar. Have not had a problem since.