Unplug the transmission secondary connector. It's a 2 pin connector on the transmission under the air intake and battery box.
Pin A should have between 1 and 4 ohms to ground. That is the pressure control solenoid (governer). Pin B is brown with white tracer wire ( the pin we are interested in) should have between 8 and 20 ohms to ground. If it's not between 8 and 20 ohms, the problem is in the F solenoid or wiring, both inside the trans.
Make sure you measure the resistance on the transmission side of the 2 pin connector.