I just finished replacing a bad 2 wire solenoid on my boat with a new 3 wire version without having to replace the entire harness and wanted to share. The 2 wire system is fairly simple in operation. The helm switch closes a relay, which energizes the red wire that goes to the solenoid. The black wire on the solenoid goes to ground, so this completes a circuit and the solenoid opens. The two solenoids are set up in a "cascade" operation where the helm switch closes the relay for the first solenoid, and the closing of the first relay closes the second relay, so there's a very slight delay built in, presumably to avoid two high current draws happening at the exact same time. In my case, I replaced solenoid #2 so there was only a power and ground wire to deal with. If you are replacing solenoid #1, you will have an Aux wire to deal with as well, but as far as I can tell the Aux post and Ground post on solenoid #1 are tied together, so I believe that the Aux wire can just be grounded instead. The modern 3 wire version of the solenoid (with the black connector) is a little bit different. This setup uses a 4 wire solenoid in conjunction with an inline time delay relay. There are actually two separate solenoids in one casing, a high-current "pull" solenoid that is responsible for pulling the flappers open, and a low-current "hold" solenoid that does exactly that, holds it open. At the solenoid itself, there is a green, white, red, and black wire. Green is the pull solenoid ground, white is the pull solenoid power, black is the hold solenoid ground, and red is the hold solenoid power. These 4 wires feed from a time delay relay. On the connector side of the relay, there are only three wires, red, black, and white. On the newer harnesses, I believe that the white wire has constant power (I haven't seen a wiring diagram for nor do I have the new harness, so I'm making an educated guess here based on the solenoid test procedures that Corsa has published), red is switched power, and black is ground. When power is applied to the red wire, the relay temporarily connects the green and black wires on the solenoid side together, which completes the circuit on the pull solenoid for about two seconds. The hold solenoid remains powered as long as the helm switch is on. After doing some testing, I concluded that it's ok for both the white and red wires to be switched, even though I believe the newer Corsa harness gives constant power to the white wire. So with this in mind, I made a pigtail adapter to go from the original 2 wire harness in my boat to a new 3 wire solenoid that I bought from a member of the Cobalt Boat Owners Facebook page. To make the adapter harness, I bought about $8 worth of connector parts from Napa: (3) NW 725171 female terminals (these are 14-16 gauge terminals, I did not realize until I got home that the original 2 wire solenoid uses 10 gauge wire. If I were doing this over again, I would by (1) 14-16 gauge terminal and (2) 10 gauge terminals) (3) NW 725440 weather pack terminal boots (same as above, these are all for 14-16 gauge wire, I would buy (1) of this size and (2) of the 10 gauge versions if I were doing this over) (1) NW 725178 connector (this will mate with the black connector on the 3 wire solenoid) I cut the wiring pigtail off the bad solenoid so I could reuse the original 2 wire connector, added a jumper wire, and terminated the loose end with the parts listed above. A picture is worth a thousand words: Note that on the black connector side of the adapter, both the red and white wires are connected together, so they will both have 12v when the helm switch is on. Even though the colors on my adapter don't match the colors on the solenoid side of the connector, I did this on purpose so the larger 10 gauge red wire would feed the white wire pull circuit on the solenoid side, and used a smaller 16 gauge wire to feed the red hold circuit since it uses much lower current. Tested this setup in the driveway and it works fine, the two solenoids still "cascade" open. One thing to note, my original harness has a 10 amp breaker installed. From what I can tell, the newer harnesses use a 20 amp breaker, so something to keep in the back of your mind. I opened the flappers 10-15 times and did not trip the 10 amp breaker, so I think it will be fine. I hope this helps someone, much cheaper to buy a solenoid for $180 than to have to buy the entire upgrade kit at $500, not to mention the work involved in removing the old wiring and reinstalling the new stuff. With the adapter harness, most of the work can be done out of the boat and there is no cutting or splicing of either the original harness or the new solenoid.
