[mr0077]

Curt, hope this upload works...see the attached photo for a very crude wiring diagram.
The easiest way would be to take the wire that now energizes the starter solenoid off the solenoid, hook it up to a power and a trigger terminal on the solenoid, run a wire from the other power terminal back to the solenoid and run a wire from the other trigger terminal to the trans neutral switch. If it is a 2-wire switch at the trans, run the other terminal to a ground.
It works like this: When you switch to the start position, power from the switch goes through the relay trigger circuit, to the trans switch and (if the trans is in neutral) to ground, energizing the trigger and closing the relay. At that point, power goes through the power circuit on the relay and on to the starter solenoid and cranks the engine. If the trans is not in neutral, the trigger circuit is never energized and power never gets to the solenoid...