Use the 92-97 ford tank selector vavle that the diesels used. They had a momentary switch that reverses the polarity to shift the valve back and forth and the frame rail mounted selector valve also has two input terminals for the fuel level gauge and one wire that goes up to the cap so when you wire it up all you have to do is run two wires down to the selenoid (since the switch handles reversing the polarity), and then tap into your sending unit wire tie the section going to the cap to the appropriate one wire on the 5 prong plug and then tie one wire from teh aux tank to one of the two remaining sending unit wires. that way when you switch tanks it will give you an accurate fuel level reading and allow you to send and recieve fuel properly from the cooresponding tank.

My last truck i did this, i bought the frame mounted valve and cut the plug from a wreck ford diesel truck in spokane, $35. drilled the frame mounted it, bought a few short pieces of rubber hose figured out how it all needed to run and added the ford in cab switch and a short piece of thier wiring tied into a couple of lead from a fused tie in.

i know im not the best for explaining but it was really simple once i figured out that the switch was a momentary switch that just needed to provide reverse polarity when pushed from one end to the other it had a + and - feeding one side of it mine were tapped into the top two holes it and then two short jumpers that crossed over each others and tied into the bottom two holes. then the middle two hole was where the two leads going to the selenoid came out of.

Good luck understanding my ramblings, but that setup sure made having two tanks and an accurate gauge on the fuel level in each of those when i would switch over nice.

 

check out Northerntool.com they have a 91 gallon transfer tank with toolbox for 600.00 and a gravity feed kit for 60.00 , if i run across some extra money, might go this route.

 

i think im going to build one with a small clearance on the bottom so i can bottom drain the tank........i was thinking of diamond pattern aluminum since it not to expensive and fairly easy to weld on a non windy day that is.......expecting to pay about 160.00ish in the materials........