[rajincajintj]

Originally Posted by hatzie

Standard Motor Products FV1 is a 3 port selector valve without provision for the fuel return line.

AC Delco 467513 is a 6 port solenoid valve and it's discontinued. Your GM dealer may be able to rattle one loose from another dealer that has one collecting dust.
Standard Motor Products FV3 is a 6 port solenoid valve. I'm unsure about its' status... It may be discontinued as well.

The tank and gauge harness is a sub-harness that can be replaced. There's a board member that has been working on producing the common motorized dual tank sub harnesses. His handle is gmachinz.

The easiest to read wiring diagram for the 1981-1991 motorized valve system can be found in the 1989 RV series schematics for the diesel trucks with dual tanks.
BTW Get the ON-ON AC Delco D7089C switch for the 87-91 TBI trucks not the Momentary-Off-Momentary switch with "Depress Fully" on the front, originally found on the 81-86 trucks.

That is very valuable info hatzie. If I go that route, I will need that. Thanks for your help.