88 Suburban Fuel Pump Wiring

[c0rey]

I got a 1988 suburban and since the day I have got it the gas gauge is pegged out and the guy ran a wire from the fuse box to the fuel pump plug(connection between the wiring harness and pump harness). I unhooked the jumper wire and here is what I got.
Unhooked there is one keyed source power wire. Ok good.
Connect the connector and the keyed source power wire becomes a dead wire.

So something isnt right here and my pump wont work like its suppose to.

The sending unit reads pegged full with the jumper hooked up, and empty with just the connector hooked in.