I am having the same exact problem with my 89. I had taken the aircleaner box out to work on the steering. I put everything back and went to start it and it only ran for about 2 seconds. I kept tryin for about 10 -12 times. I finally took the pump out and tested it, it was fine. I check relay, it was fine. (actually put a new one in to be safe)

I tested the the relay ports with a multimeter. It barely moved, so I am thinking there is a problem with the power into the relay.
Dont know where to go from here.
I thought I would ask if you ever figured out what is going on.
Thanks,
Scott