Im not to fimiliar with the older nissan diesels but im sure its pretty close to the newer unicarriers.

F-85 is a code for the forward 1 solenoid.
Below 250mA for 1800ms or above 3.8A for 200ms. Output from vcm is shut off.

F-87 is a code for the forward 2 solenoid for two speed transmissions.
Below 250mA for 1800ms or above 3.8A for 200ms. Output from vcm is shut off.

Wiring for all 3 solenoids should run to the VCM which is behind the RH steps black cover.

Disconnecting the solenoid connector then trying to check for voltage is not possible. VCM will cut power to the connector when it finds a fault and throws a code. Connections should be back probed while connected to check voltage and amp clamp while plugged in to check amperage. Codes will need to be cleared before this can happen as well.

Does this unit have an analog dash or does it have a digital display