You don't really need a kit - I don't think anyway.
There are only 3 wires that go from the cab to the actual tank switching valve. A dark green and a light green that come off the dash mounted switch. One powers the valve CW and the other powers it CCW (IDK which one is which).
There is also a pink wire for fuel tank level indication on the dash. It is the same as a single tank setup all the way to the Pollak valve. At the Pollak valve it splits off into 2 wires. A pink/white that goes to the production (drivers side) tank and a pink/black for the auxiliary tank.
When the tank is switched over, the sensing line also shifts to that tank.