Hi XXXXXXXXX, the first thing to do is make certain the engine is free to spin over. If thats checks out,make sure you are getting power to the S terminal on the starter motor when the key is held in the crank position. If not,trigger the circuit would need further testing.If it has power,you need to check for proper voltage and ground at the starter,by doing a voltage drop test. I will send you a diagram that shows how this test is done on a starter circuit.
Auto Mechanic
worked for NYPD 30 years as mechanic on these type vehicles