Originally Posted by Team G
Have power to starter,( on heavy cables)all dash lights function, yes, in neutral. Issue seems to be no start power on wire to starter solenoid. As if something is saying, don't start.
If you run a jumper wire ; watch for sparks ; from the main cable to the solenoid wire , will the engine turn over . Doing this will confirm the starter is operational, done with the key on the engine may start.
As far as the location of the starter relay , it should be between the batteries and the starter , can you follow the wire from the solenoid on the starter back to the relay.
Here's the info on the starter relay on my old F/L chassis , yours may look similar.