[blown240]

Do you by chance have an aftermarket stereo? They have a constant hot wire so that they don't loose their memory. They also have a wire thats hooked to the dash lights so that the radio will dim when the lights are turned on. I could see that if the grounds were not good that something strange could happen here.

When you did your grounds, did you get a solid battery to motor and motor to cab? Or battery to cab. Also check the ground on the stereo, if you have one.