1996 Isuzu Hombre Fuel pump no power

Driving down the road shifting to second gear truck just died then will start but shakes and acts like it jumped time didn't hear fuel pump kicking on so bought new pressure is good but leaks down to 0 after a few min but every now and then will get pressure but not enough to run good checked spark and all four cylinders are getting fire checked fuses all good relays have not checked yet getting.5 volts on the 3 wire harness but grey wire that should be power to fuel pump is dead don't know what else to do at this point cleaned all spark plugs and took fuel injectors out cleaned them as well and hooked all back up and still runs like crap
wanted to know what if I hot wired a power source direct to fuel pump would that mess up my new fuel pump if it got a back feed at some point !
Also noticed one head light dim and on when I turn key on but I did take bed off and disconnected a few wires but nothing that should be shorting out light WTF !
Thanks Steven Turner