Solenoid
I put a piece of steel that I cut and drilled to fit between the starter battery terminal and the terminal that normally has the wire from the ignition switch. The cable from the starter terminal goes to one large terminal of the solenoid. The battery cable from the battery goes to the other side of the solenoid. The small wire that went to the Chevrolet solenoid goes the the Ford solenoid. The batteries need to be hooked up in parallel. The positive from one battery goes to the positive of the other battery. The same with the negative then you ground the negative cable to the frame. The positive cable then goes to one post of the battery switch and the other goes to Ford solenoid. Wire it into the system and you're set. Hope this helps.