Helping a freind try and fix rear fuel tank and gauge not working on his E350. Electric fuel pump is new, and powers up when key is turned on. front gauge and tank works fine. Any help in a direction would be a big help.

 

The info on your post is not clear.
Do you hear the rear pump run at all? If you remove the rear tank fuel cap and turn the key on , do you hear the pump run for the usual 2 seconds? Don't know what year the vehicle is.
If the front pump is working OK would suspect switch on dash or possible wiring problem to rear tank.

 

91 E350, the fuel pump is mounted to frame just behind driver seat. When key is turned on, regardless position of switch, the fuel pumps fires up.

 

That pump you are referring to is the high pressure pump. It serves both tanks. There is a fuel pump in each tank. If the gauge for the rear tank isn't working, either it is empty or the power from the dash switch isn't getting back to the tank unit. With the switch in the rear tank position when you turn the key on you should hear the rear tank pump run for the 2 seconds. Does it?