How to wire 1986 chevy truck dual gas tanks - 1500 Chevrolet Cars & Trucks

SOURCE: 1992 f-150 dual gas tanks tank closest to cab of truck pumps gas out the fuel cap

A FORD EQUIPED WITH DUAL TANKS THIS YEAR MODEL HAS CHECK VALVES IN THE FUEL PUMPS .THE FUEL RUNS FROM THE REAR TANK WHEN IT IS POWERED ON TO A TEE AND INTO THE SAME LINE AS THE FRONT PUMP . THE PROBLEM IS AT THE BOTTOM OF THE FRONT FUEL PUMP THERE IS A CHECK VALVE ON THE FOOT AND IT IS NOT WORKING.WHILE THE TRUCK IS RUNNING WITH THE REAR FUEL PUMP ON IT IS PUMPING FUEL INTO THE FRONT TANK . IT WILL RUN OUT OF THE NECK WHEN IT IS FULL.THE FIX IS SIMPLE REPLACE THE FRONT FUEL PUMP. THEY DONT MAKE A CHECK VALVE REPLACEMENT I CHECKED I HAD THE SAME PROBLEM AS YOU.

SOURCE: 1982 chevy truck with dual gas tanks with guage or tank problems

all you need to do is listen to hear the tank switching valve is working. It will make a soft noise under the rear cab section with the key on with the engine off. zif you do hear it sounding the switch your tank unit for that one tank you try to switch to is a fault. Sorry no illustrated diagrams are on hand, just knowledge