Bassmat, you seem to have a good knowledge of testing,
if tha diagram provided by JD5210 is correct, remove the fuse for the "fuel shut off solenoid",
then test the " ignition side of the fuse" for a short to ground, if this doesn't short to ground, then you know your problem is on the other side of the fuse, The wire to the solenoid relay or to the solenoid on the pump itself. You can then disconnect the solenoid on the pump and do your test for a ground "again",
this will eliminate the solenoid on the pump. do the same for the relay, my guess is thats it a grounded wire in that circuit that has lost some of its insulation, been there, done that.
Good luck