Double check the key switch connections. Tug on each one of them, and also tug on each connection at your lanyard/kill switch.
Check the alternators really well.
I don't know if a Rinda/scan tool will be of much good for you on this one.
If you can't find anything wrong, can you isolate each motor to a battery? Thin chance, but it can happen.... you could have a loose connection IN your battery as in loose plate(s) or something else going wrong.