I have a 75 d200 with the 318. I put a electric fuel pump on it the other day attached to a switch and since then the battery has died pretty fast with everything off. I put a new battery in but it kept dying so I changed the alternator and it still just cuts off anytime I unhook the battery terminal. Any thoughts?

 

You have verified the fuel pump shuts off with the ignition?

 

Fuel pump is connected to a switch I make sure is off after the ignition is off.

 

After I jump the truck off it runs for 3 minutes or so and dies and can’t get it to start again due to battery

 

If the alternator is charging it sounds like the battery died, pull it and have it checked out.