So far I have tried the following:1) Charge and test the battery at NAPA -- battery tests out "Good"2) Test starter at NAPA -- spins easily, sounds good3) Removed starter solenoid cover -- oil on contacts, contacts and plunger are pitted. Cleaned and sanded contacts4) Clean and tighten battery terminals5) Clean main engine groundThe only idea I have left is to remove the positive cable and ohm it out to see if it has a broken connection.The starter contacts do not look like new, and are probably 8 years old. Is it possible the starter will run for NAPA but won't on the truck because of contacts?Thanks in advance for your help.

Are you getting 12V to the solenoid terminal when the key is turned to START position? Possibly a key switch issue. But you could do a voltage drop test...

0V at solenoid terminal when in START position. Do you mind giving me some pointers on how this works? Is this likely an electrical problem with the ignition switch? I see a rod moving when I turn the key. All the accessories work when the switch is ON, and the accessories go off when the key is turned to START.Looking online at the part picture, I think I replaced this part several years ago

fuseable link fried? have you checked all fuses?

Wiring diagram is a bit crude but it should help out...So check the starter relay and then check to see if there is 12V from the yellow lead from the ignition switch... It might also be a safety switch like clutch or auto trans safety...

Thanks for the replies, very helpful.I found several pics of a starter relay, but haven't found one on the truck. Could I get a hint where this is located?On the right side of the wiring diagram is a rectangle marked "31". Is this a fuse or fusible link? Any idea where this is located?Thanks again.

I think 31 is a connector...Fuseable links are just forward of the starter relay and the starter relay should be mounted on the driver side fender.

From the starter relay connector (starter relay removed), I have 12V when the key is in START on the yellow wire, from the ignition switch. I also have continuity from the starter relay connector to the starter solenoid terminal (brown wire). So the starter relay ($12) is suspect, and I will replace that next. It looks to be original. and I haven't replaced it in the last 10 years.

Sound like you got it pretty well figured out now!