Review on Adjustable Driver Controller - Uniquegoods 1803BKW Model by Jose Strong

Bought two, trying to get one to work with a 12vdc RV fan. The fan ran on 12VDC at 1.75A at full speed. The fan thus fulfills the specifications of the controller. My RV's fans are turning on and off (and they're still running) and I wanted to lower the speed in the evening or at night so they wouldn't be as noisy. 4-wire connection, simple. Battery power, mass, fan power, mass. Well, the fan is on no matter what speed the potentiometer is set to, even OFF doesn't turn the fan off. The red LED on the board will illuminate, but the ESC will continue to conduct power. Not as expected. So I tested both PWM controllers and found that they really work. Here is my problem. The builders of my RV decided that running two separate wires from the fan and vent to the panel was too much work, so they did the ground together (one white wire). This is a problem for the PWM controller, the ground cannot be shared between the supply voltage and the load (fan motor). PWM controller. Then I have my own 12.6V DC power supply on the panel, plus two wires for the fan and no common ground. This complicates the decision as one of my fans is routed through an exterior wall and surrounded by polyethylene insulation. I don't think a snake is possible. I hate spending hundreds on remote fans.