There should be a grey one wire connector on the firewall near the brake Hydroboost. That should be the wire going to the starter solenoid. Jump B+ to the side closest to the engine and see if it cranks. If it does, do a voltage drop on the positive and negative battery cables while someone is cranking the engine over. Measure negative post to good ground on engine, and positive post to starter stud (not the wire, and not the nut, the stud itself) on the driver side battery. Also measure positive crossover cable from post to post. You are looking for less than 1/2 volt per cable.