1990 Mustang GT Not starting fuel pump not running?

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Posted via Mobile Device it should be close to battery voltage at some point during the prime cycle. Once again, you have everything needed for the pump to run properly. You need to unhook the connector on top of the tank that's for the fuel pump. With that unhooked, and the fuel pump trigger grounded, THEN test the voltage at THAT connector with the key on. If the voltage is now battery voltage and not the low voltage it once was. Then the pump is the prpblem most likely.
 
Posted via Mobile DeviceYou would almost have to get 12v with it unhooked.

Look at it like this. The Load side is 12v or so. So when the relay engages, then 12v or so will be fed to the pump. So it would have to be the pump dragging causing high amps to drag the voltage down. Its just not bad enough to pop a fuse link. YET! Or it could be a bad wire going to the pump.