I hate buying an old truck and seeing a break controller. You can about guarantee there's some wiring butchery. Which is so sad when you can buy a nifty adapter that plugs into the factory harness.Ground wire for my ‘91 is on the driver side frame rails out mid way down the tank. But who knows what some previous owner did.
The butchery I’ve seen of people installing trailer wiring I wouldn’t be surprised to see somebody hack the fuel pump ground.
....... WHAM