SnowDogg Part # 16160410 - HT300, HV600 HPU Relay Motor Power Unit Solenoid is used on all SnowDogg plow setups which have the HT300 or HV600 HPU hydraulic units such as the HD, EX, VX, and more. The relay motor solenoid is found on the vehicle side, most commonly under the hood near the battery on your truck. This is the solenoid which sends electrical current throughout your plow's electrical system as needed. You'll find wires such as positive, negative, and your control harness connected to this solenoid.