Why does the power to your 1986 Nissan 720 truck fuel pump keep cutting off and on?

Answer 1

check fuseable links in wires located near the battery, they burn inside the insulation, so check them with a test light. peace on Fuel pump relay is bad, located under passenger seat or under truck under passenger seat? hard to find. I had the same problem on mine! The relay is on the passenger side behind the right knee panel (just under the dash on the right side immediately fwd of the door's fwd seam). A new one was about 35 dollars from the dealer. It is aplug and play affair and took about 3 minutes to knock it out. I've had multiple 720's with 'failed' relays. The relay itself is OK, but the connections to the relay on the circuit board fail. If you're adventurous, the fix is easy. After locating the and removing the fuel-pump control relay (see above) remove the circuit board from the black plastic box. The two connections on the circuit board that connect to the coil of the actual relay fail by cracking. They are located at the end of the relay with only two connections (the other end is the contacts and has three connections). If you look with a magnifier, the cracks are obvious. When the cracks are gone, the problem will be gone too. Resoldering mine fixed my problems permanently!