cluster wiring plug 1977 gmc

[hatzie]

The 1981 and later motorized valve system only uses five of the six positions on the valve Weatherpack.

This is an electrical schematic of just the Pollack Motorized valve.


You can see terminals D & E on the Weatherpak plug go to the motor to switch the valve from tank to tank.
Terminal B is the common of a SPDT (Single Pole Double Throw) switch. GM calls this the METER SWITCH. Terminal B should run to the gauge. In 1977 this is a TAN wire running from the dash switch to the RH frame rail disconnect. You can probably find the original disconnect plug or at least this wire next to the starter on the RH frame rail.
Terminals A & C should be your sender wires from the tanks. Originally these ran to the dash switch on a 1977. With the motorized valve they should run from each sender and each sender wire should terminate at one of the Weatherpak valve plug sender positions.

How much of the original 1973-1980 NL2 wiring is still present and unmolested?
If, and only if, the original valve wiring is still present and accounted for... the minimalist solution would be to keep the original wiring in place and use a pair of SPDT Bosch Automotive relays to control the valve motor. This method only requires that you interrupt the solenoid valve power wire from the switch and add two new wires from the cab to the motorized valve D & E plug positions and the relays can be hidden inside the cab. The 1973-1980 dash switch would still control the gauge and the relays would trip when the switch is set to AUX.


If the tank sub-harness wiring is already chopped up... Here is the the 1989 Diesel tank valve wiring schematic you can use to roll your own wiring. Wire colors will change from year to year but the basic from-to will not.