Nissan Repair: Truck troubles, nissan pickup truck, fuse blows

Question
QUESTION: We have a 1988 Nissan pickup truck and we have replaced the fuel pump and we have checked for pinched power wires, the fuse for the pump keeps blowing,what could be wrong?

ANSWER: Hi Heather -

Can you tell me a couple things?

1. Was the fuse blowing prior to the fuel pump replacement?

2. When the fuse blows, does it take a while, or does it burn immediately?

Please get back to me -
mahalo and aloha
calvin

---------- FOLLOW-UP ----------

QUESTION: Hello Calvin,

Yes the fuse was blowing before the pump was changed. Also the fuse burns immediately. Thank you for helping me!

Answer
Hi Heather =

Thanks for replying.
If the fuse is blowing immediately, you have a direct short somewhere. If you have a voltmeter and 12V light tester, then I can walk you through a diagnosis. If not, then it is better to take it in to have it diagnosed.

Anyway, what you are looking for is a hot (wire that is energized when the fuel pump is on) lead that is grounded somewhere or fused to another wire. This requires that the entire wire be traced back to the fuse box from the fuel pump.

To help the diagnosis (you will need some fuses, though), you can disconnect the fuel pump, disconnect the relay (should be located in the engine compartment), and disconnect the lead that provides power to the fuel system (you can also disconnect the battery). After all that is done, put a fuse in. Connect the battery and check to see if the fuse is blown. If so, then you are looking for a short somewhere before the relay. If not, then connect the relay back. If the fuse blows, check wiring between the relay and the fuse box. If the fuse does not blow, then connect the fuel pump back. If the fuse blows, then check the wiring between the fuse box and pump. This is simply a process of elimination -

Hope this helps -
aloha
calvin