Starter Relay 90 Sport

I'm trying to fully understand your question. Does your new relay have an additional post that your old one did not? And, why so many relays, you're not running a deep cycle battery are you?

This wiring schematic put together by TRBenj should help a little bit. In short, yes, the red and yellow provides switched power, which originates at the key, but the tranny has to be in neutral (and the neutral safety switch working), because that is another switch.

So, switched power goes to another switch, which goes to your relay:

Hopefully Pete Brainard or someone will weigh in here as I don't have a picture of my own relay handy. But I don't think that 4th post is supposed to be a ground. I've done some casual poking around old posts, and the relay is supposed to ground itself somehow on the metal block it's fastened too. And I guess it's important to keep that contact point clean.

Obviously, one big one is for the positive coming from the battery, and the other big one is for the positive going to the starter. And, one little one is for that red yellow wire coming from your neutral safety switch.

In some marinizations (not typically PCM) the ignitions is setup so the distributor (or coil) gets full, non ballast resisted, voltage, only when the engine is cranking, then normal, resisted voltage after the starter is released. My theory is that is what that other (I) post is for, but not used with the PCM marinization.

I'm going to take a stab and say that maybe you had your red and yellow going to the little (I) post and not the little (S) for starter post. If you look at Tim's diagram above, he show the I post just hanging out not doing anything.

Eric,
Brian summed up the 4 posts on a typical relay very well.

You state the relay you got is an isolated base so I feel you are heading in the proper direction with finding the terminal for ground. It's best you get the Ohm meter out and confirm which two terminals go to the coil. Then, if in fact the base is not the ground source, you need to make up a jumper wire to the block.

Sounds like you're on track. Keep us posted.

running the stereo gear on a deep cycle is fine but its not the right battery for starting that big ole ford iron.

Ground wire was the fix.... Here is the old one... It was grounded to the base...

Eric,
Those contacts look pretty bad but I'm glad you got it fixed. I hope it stays fixed. A couple things to keep in mind with burning up relays. We already discussed deep cycle batteries being bad but the other is a starting battery in poor shape or run down on it's charge. Both will cause the same problem. It's low voltage causing a high amp load across the relay. (Ohm's law) So, never use a deep cycle battery as they do not like a high amp load and the volts will drop and the other is keeping a good starting battery in good shape/charged.

When you store the boat, is it for extended periods of time? Maybe you have a parasitic load draining the battery? Have you checked for it?