Just posting an update here, which I'm copying from the pre-1997 board:

"I replaced the starter relay, tried to do the cable that goes between the relay and the starter, but couldn't find one. The auto parts store don't carry one so I might get one this week at the Ford dealer. I noticed there was some corrosion underneath one of the outlets on the relay, it was the outlet that has one of the cables that go to the starter.

So far so good today, I've been driving it running my errands and it's started perfectly each time. I'll get the cable I mentioned this week if my problem continues.

Thanks to everyone who responded, especially PKRWUD."