Hello All,
Im new to the fourm and could really use some help. I have a 98 Express 2500 5.7l that wont crank. I have replaced the starter and relay to no avail. I pulled the starter relay and verified constant power, ground, jumped the sockets and got the starter to engage do the wiring to the solenoid is good, put it all together snd nothing. Also verified that the ignition switch sends power to the relay when turned to start position(used test light). Im really stumped. Could use some of your wisdom.

 

There are 2 small studs for wires on the starter solenoid. Possibly you have these reversed. Put your meter on these wires and see if you get 12 volts when the key is turned to start. If you don't get 12 volts at the starter then there is a problem with key switch or relay.

 

Check the park neutral switch. Could be showing the van in reverse instead of park.
Also, does your van have an imobilizer? Check that if so.
My money is on the switch.