The purpose of this post is to help you select which trim relay board is best for your situation.
If you have both elevator and aileron trim and you are considering actuating your wing flaps or speedbrakes from a stick grip, you definitely need the 3-channel trim relay board (TRB). One channel is required for elevator trim, one for aileron trim, while the third channel is needed for the flaps or speedbrakes.
If you have a stick grip (like the Infinity shown here) and want to use all of the switches/buttons, you need the 3-channel TRB with the 15-pin connector. The Infinity grip has a 4-way switch for elevator and aileron trim, a push-to-talk switch (the trigger) for radio transmissions, and 4 additional momentary buttons that can be used for a variety of functions. Because of the number of grip functions, you actually need the 15-pin D-sub connector to serve as a hub/gateway for all of the switches. You would not actually need the third relay channel, but it could be used as a backup in the event of a failure of one of the other relays. To use the backup relay channel, however, you would need to re-pin the connectors accordingly.
Now if you have two maxed-out Infinity grips with all the bells and whistles, you will definitely want our newly introduced ‘The Ultimate,’ which is designed specifically for this situation. With its two 25-pin D-sub connectors, there are plenty of pins for all the ground wires (you will probably have about 12 total) plus there are individual connections for each of the copilot stick functions that work in concert with the pilot’s functions. And the 3 relay channels will accommodate two axis trim and flaps on both grips.
If, on the other hand, you have just one grip and you only have the 4-way and a maximum of three additional switches (such as the PTT, IDENT button, or autopilot CWS, for example), you could get by with the 2-channel TRB with the 9-pin connector. The 9-pin D-sub connector is sufficient to handle all of these functions. One advantage of using the 9-pin D-sub connector is that, if you should desire, you can actually have a disconnect for the stick grip located inside the stick tube, thereby allowing you to easily remove the grip for maintenance. A pair of modified 9-pin D-sub connectors will fit inside the tube of the stick grip in most installations.
To review, if you have a 4-way and 3 or less additional pushbutton switches, you should choose the 2-channel TRB. If you have a 4-way and more than 3 additional pushbutton switches or if you plan on having a flaps or speedbrake switch on your grip, you should select the 3-channel TRB. If you have two grips of any flavor, you should try The Ultimate for maximum ease of wiring and accessibility.