Had a similar problem. Here is what I found. The GP's all checked out good, had voltage going to and from relay (when activated). It drove me crazy till my Indy asked to look at the "inbound" + wire. The wire was capable of carrying +12V but not capable of carrying the amperage needed to activate the relay as the wire inside the shielding had deteriorated. Replaced that wire and all was good again.
just my .02
and a good lesson for me.