Load test the battery to make sure it is still good and fully charged. Inspect all of the "big wires" from the battery to the motor to make sure everything is clean and tight. Look for a missing ground strap, and check that the ground connections are on clean metal with no corrosion or paint to interfere with the connections. The problem must lie between the battery and the place where you connect the jumper cables. Either side can cause this meaning you must check the electrical path of both the hot side and grounds. David Teitelbaum vin 10757