Re: 24volt system 12 volt TM
Use a continuity tester to track which wires from the battery side feed which prongs on the front plug. You may find both reds and one black extends to the plug. Remove the receptacle from the boat where the plug attaches and look for the fourth wire, it may be bundled just inside. You could cut the plug off and wire the three leads (plus the fourth if you find it) to a Perko (or sim) 2 Battery Switch. You could probably mount this in the location that the Run / Charge TM switch is located. It will allow you to switch between Batt 1 feed, Batt 2 feed, Both batteries or None. The Both setting would drain both batteries in parallel, which should provide the longest 12v service time.
If you can't find but one ground / black wire fed to the plug, connect the NEG terminals of both batteries together (do not use a battery Integrator or Isolator on this circuit, they will disconnect your batteries whenever you are not on plane). Now your black / ground wire from the batteries (attached to both battery's NEG post), is feeding the Perko switch and should work fine.
As always, check your setup's output with a voltmeter before attaching equipment. You should get 12v on three of the Perko's settings and 0v on the None setting.
Be sure and install two accessible fuses on both of the red / power feeds from the batteries (manufacturer of the TM would tell you want amp fuse to use).
