Chevrolet Repair: 1987 chevy pickup, jumper wires, jumper cable

Question
fuel pump will not run off the pickup system if i put a jumper off a battery charger it will run if i put a jumper from a 12 volt source on the pickup it does not run i checked the ground with a test light seems to be okay  i have been working on cars forever it seems this one is werid  thank you Roger Nelson

Answer
Hello Roger,
Try using jumper wires from a different good battery, to both wires of the pump.
The battery charger may be puting out more than 12 volts. The pump won't run on much less than 12 volts, but that way you can see if it will run on 12 volts.
The ground wire connection at the frame needs to be clean and tight. Also the ground from the battery to the frame, which may depend on a strap from the block to the firewall. To check that, connect a jumper cable from battery ground directly to the frame.

Van