Crank Fuse blowing

I have a 2000 GMC Sonoma, 4.3L, A/T, 4WD, the 10A crank fuse blows on a regular bases. A mechanic stated the Park/Neutral switch and it's joining connectors was burned up so he replaced them. The problem still persists. The load side of the fuse goes to ground. Thinking it was a problem with the wiring, I ran new wires to the P/N switch and the 4WD control module. This didn't help. By accident, while using a test lamp, a put +12V onto the load side of the crank fuse while it was showing shorted to ground. The starter briefly indexed and the short went away. I have since replaced the starter, which the auto parts store stated was bad, but the problem still comes back. I also replaced the ignition switch. When the problem is there, I can always make it go away by briefly touching the load side of the fuse with +12v.