Righto.
I double-checked the relay I found under the hood (over the passenger fender in the fuse block box), and according to the awful Chilton manual I have, this *is* the starter relay. (I say awful because, for example, the picture that matches my truck is for the 4Runner, while the picture that is supposed to by my 1991 truck does not match what that block looks like at all.)
I would very much like a copy of the wiring diagram, even for future use. If I cannot find one online, I will email you with my mailing address, if you really don't mind putting it in the mail.
I just got back from PepBoys where I was going to pick up a new starter relay, but they have to order it, and it will cost close to $30 by the time they slap CA tax on it. I was thinking it was going to be $10 bucks. Not that I mind $30 if I know it will fix it, but if it doesn't I will have to buy other stuff, so I either want to find a cheaper vendor or test this relay somehow to see if it's actually bad. Thanks again for all of your help!