How To Prevent Electric Over Hydraulic Actuator From Drawing Power from Trailer Battery

Updated 01/19/2026 | Published 01/11/2026

Products Featured in This Question

Hydrastar Disc Brake Kit w/ Actuator for Tandem Axle Trailers - 12" Rotor - 6 on 5-1/2 - 6K

(33)

$1743.35

Roadmaster Single Park Light Diode

(136)

$21.23

Question:

Hi, I bought this HYD44VR kit for my 2018 Cougar 311RES fifth wheel and just finished wiring up the controller. Im using the 12 volt positive from my 7 pin harness that connects to my truck. This 12 volts is also connected to my fifth wheels internal battery, so the 12 volts going to the Hydrastar conntroller is ALWAYS hot, not just when my trailer is plugged into my truck. Is this going to be a problem? Always having positive 12 volts going into the controller? Thanks, Steve Holloway

asked by: Steve H

Expert Reply:

Hey Steve, to avoid having the trailer battery power the actuator of the Hydrastar kit part # HYD44VR you would want to install a diode that only allows the current to go to the battery and not from the battery back to the actuator. For that you'd want the part # RM-690.

expert reply by: Jameson C

Howard

1/14/2026

Hot wire for power to Hydrastar controller should come from coach battery. I haven't had any problems with draw on battery or anything.

Steve H.

1/18/2026

@Howard I didn't want the Hydrastar to be continuously be "powered on" if it was always connected to the coach battery. Since my trailer only needs brakes when moving, I wanted to have the Hydrastar "hot" wire connected to the truck when my 7-pin was plugged into the truck. I was able to achieve this using the RM-690 part described above. The RM-690 only allows power to flow in 1 direction, so the truck can charge the trailer battery, but the RM-690 doesn't allow trailer battery power to go back to the truck. I have the Hydrastar "hot" wire connected to the truck power with the "IN" side of RM-690. The trailer battery is connected to the "OUT" side of RM-690, so the truck still charges the trailer battery when traveling. The "breakaway" wire of the Hydrastar is powered by the coach battery (through the breakaway switch) when the trailer's breakaway switch is pulled, so the brakes work even if the trailer detaches from the truck. Steve