I have a 1991 GMC stake body truck that will not crank battery are fully charged .When ignition switch is turned to crank there is no power to the starter solenoid purple wire. Jumped the purple wire to B+ and the truck starts and runs. I Replaced the starter relay and still will not start I need to know where the neutral switch is and where the ground is for the starter relay . I am having a hard time getting a hold of a wiring diagram for this truck . Thank you for any help you can give me !