Hi There
I have a wiring diagram for this truck, but I think the problem is mechanical. The contactor you talk of is a line contactor and has a plunger pulled in by a coil, these plungers can get crappy under the battery and can act ''slow'', hence the hammer cure will jump them into action. Pain in **** job as you need to remove the battery and remove coil assemble. then take out the coil assemble. 2 wires and 2 cables. you will see two 2ba bolts on the coil ''H'' frame remove these and clean up the plunger and wipe out the coil tube check that the stop on the ''H'' frame is not worn back by the plunger. This will also cause the same problem. contact me if you require further help