89 E350 cutaway (motorhome)...no fuel frm tanks...I need help!!

I have a 89 motorhome using the E350 chassis with a 7.5 liter engine. The unit has 2 fuel tanks and neither of the tank fuel pumps are engaging. I have replaced the relay switch inside the drivers side front fender, still nothing. There is no constant power getting to the relay switch with the ignition turned on however, one of the brown wires coming from the relay has 12 volts of power when the tank selector switch is moved to the "forward" tank. Then, when I switch to the "rear" tank I have no power at all to any of the wirse leading from the relay. When I switch between tanks, I hear a "mechanical" sound and followed the sound to a mechanical switch located inside the drivers side frame rail. So..... I have at least identified the mechanical switching mechanism and have replaced the electric fuel pump relay switch. I have further discovered I have no constant power to the relay when the ignition is on. Has anyone else come across theis condition and can offer some ideas? Thanks, Steve