Usually, the access point for the supply is the rearmost connector before the harness goes up 'n' over the tank. The ground is usually a separate, single wire with a screw connecting it to the frame.
I built a one-foot "extension" harness using Weatherpack connectors and pins, and some plain ol red 14-gauge wire. I can poke holes in the extension harness for test probes and not have to worry about the vehicle harness corroding.
Don't have a good photo of it. Just barely visible at the bottom of this picture. There's no good access to the pump ground wire except at the frame, unless you take the bed off..
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