For anyone that's heard or read about 2012 model year Mastercrafts, you will know that the control system was different from years before and years to follow. The largest challenge I faced with the control system is that the ballast timers were incredibly difficult to modify. While it was technically possible, it took a specialized programming tool of which there were allegedly only 3 in the US. This meant that you could not add bags, change the vent arrangement, and increase fill times like most other model years. Some people were able to fake the system into thinking it had the factory piggyback arrangement which used motorized valves (read: unreliable). Others attempted to control the factory pumps with a second set of controls in parallel with the main system. I chose option 3: Additional Pumps.
This project went through two different phases. In the beginning, I ran the piggyback bags as completely separate ballast locations. The only interface with the factory system was a Wye in the thru hull and a Tee in the vent. Otherwise, they were totally separate. The challenge with this approach was that the factory controller would default to listing the boat leaving a full bag on top of an empty tank. In addition, the factory controller would sometimes fault and I'd be forced to cycle the switch repeatedly to drain the tank completely. This drove me to update the plumbing arrangement (which I've posted here about before) to the following:
While I only ran this arrangement for a few months before selling the boat, I can say it worked well. The new pumps acted as the primary pump to fill the tank and bag and the factory pump acted like a booster for the time period it was programmed to run. The end result was slightly faster overall fill/drain times because of the optimized pumping capacity and I never again had an issue with full bag on empty tank.
Knowing resale was in the future, I wanted to make it look as factory as possible. So, $30/switch later, I had factory Starboard and Port Ballast switches. I used a switch/relay arrangement and built a relay box using a poly case enclosure and automotive relays. I bent a piece of 4" wide 1/8" thick SS for a mounting bracket and tucked it up underneath the overhang for the rear corner seat so water wouldn't drip directly on it and power / pump wire distances were fairly short, but the box wasn't in the engine area. If I had to do it again, I'd consider using small 2-channel relay boards in individual enclosures mounted near the pumps. I think this could make some parts of the project easier. Either that, or the same modules, but in a single enclosure together instead of individual automotive relays.
Test fitting wire lengths
Seeing if it all fits in the box. Circuit breakers were mounted to the box and I used cord grips / Deutsch connectors for control and pump terminations.
Tucked away on the starboard side.
I've posted on here, but I also used a small 5 amp timer relay in the drain control circuit to give me timed drain since it empties below the waterline.
The factory pumps are mounted on small platforms that attach to the transom and they offer good service access, so I used a 5" x 5" section of aluminum square tube to make a riser for the new pumps for similar hose routing and impeller access.
For bags, I chose to go with Sumo 650's. While they aren't technically the biggest that can fit, they were fine.
This was a fun project that happened in phases over the course of a couple years. When I sold the boat, I was very happy with the way it performed and wouldn't hesitate to do many of the same things again if the next boat doesn't have a complete factory system to my liking.