UPDATE - F53 external fuel pump install FINISHED

My 1990 E350 EFI 460 Class C has two fuel pumps - one in the tank, and a high pressure pump that feeds the engine.

Both of these are on the inertial switch circuit. This is so that in a crash, the fuel pump does not continue to pump out gasoline through potentially ruptured fuel lines and cause a fire hazard.

Hopefully you wired your new pump into that same circuit. Otherwise you may have a safety problem in a crash.