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Push button starter eh; that raises a couple of issues. Firstly, the relay might no longer be in-circuit - he might have fed 12 volts to the switch and then straight on down to the starter solenoid, bypassing the relay altogether - might have or might not - you'd need to follow the wiring to verify that. Easiest way is to go to the starter motor and follow the thin wire backwards and see if it comes from the starter relay or direct from the dashboard switch.

Second issue is that if it's an amateur installation then it might have failed due to poor wiring - I'd probably remove the switch and see if there are any uninsulated wires or connectors at the back which have become crossed, and are shorting out against each other.

I'd take a guess that the starter motor assembly will prove to be good, and the fault will be in the wiring. If that's the case then you can quickly put the truck back into use by temporarily fitting your own manual start wire and sort the wiring out later, especially if you need it to travel to work.