Often customers ask us how they can add a reversible pump to the existing factory MUX switch in a 2007 or newer Malibu boat. Although we strongly suggest adding any additional ballast pumps to a dedicated 3 way ballast rocker switch it is possible to use what is already on the dash.
The system configuration is possible when a pair of relays are wired to take the brunt of the load. This isolates the factory digital MUX switch and minimizes the chance of the load heavy reversible ballast pumps interfering with the factory electronics. Each relay will distribute power to the pump opposite of one another to reverse the polarity in order to run both forward and in reverse.
You will need to two Waterproof SPDT 30A Relays as well as both 16ga and 12ga. The thicker wiring will be suitable for powering the relays and the smaller stuff will activate the relay at the MUX switch. For safety we use a 20 to 30 amp fuse on the positive lead from the battery.