What engine and date of manufacture. Relay or PLC truck.
Newer PLC trucks relay 9 controls the 6 port change over valve.
Power to pin 30 on relay 9 come from F4 20amp.
Pin 87 goes to the coil on 6port valve.
PLC board applys power to relay 9s coil either on 85 or 86. Cant remember. And the other is grounded. After it recieves the signal from the rear 90 prox.
If you have the owners manual for the unit I suggest you run through the PLC diag as its easy to confirm if the PLC can output and turn on the valve as well as confirm that its getting the signal from the prox switch.
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