[wslade2]

Thinking about this problem I am going to compartamentalize.

When hooked up to the mule, system works fine. When hooked up to engine driven pump, it doesn't. Sounds like (at least now after your switch repair) everything from the firewall back works ok-because it does on the mule. The pump has been overhauled. Provided the overhaul hasn't failed, or the pump is not being spun at adequate rpm (unlikely), your problem is basically between the pump and firewall. Not much there, except the connections.

In one of my other lives, having dealt with heavy duty diesels, it's amazing what impact a fuel line suction leak can have on operation of the fuel pump and engine. ie-a little suction air leak into the fluid stream can dramatically reduce the fuel pump output.

Maybe check carefully your suction line. Maybe pressure test the suction line for leaks? What I also recall is that the fittings on the pump involve compression nut, oring and a teflon back up ring. Are these all in good shape/new? How many years has that o ring been compressed under that nut loosing some of its sealing capacity?

Also when you switch from mule to engine driven some air can be introduced.