MGL Avionics is a cutting edge company serving the amateur home built aircraft market. They are a South Africa company with offices in a number of countries.
One of their advances is the development of their CAN bus.
The CAN bus is a two wire high/low signal protocol communicating at 250K baud.
Each of the MGL components – their mini EFIS, engine monitor, RDAC, AHRS, compass, and autopilot servos – are designed to communicate using the CAN bus. This means it just takes two wires to send and receive all the information needed from each unit.
Compare the MGL wiring of an autopilot servo to one of the popular industry leaders. MGL uses two wires and the competition uses five or six wires depending on if its the roll vs. pitch servo.
Now, to be fair, you still need power and ground wires and MGL recommends grounding back as the main power bus that serves the EFIS or other instruments.
So here is a trick to simplify using the various MGL components …
If you buy pre-made harnesses from MGL for any of their CAN bus connected electronics, they use the MSD 2-pin connector. That still leaves you finding a solution for the power and ground.
Consider building your own, using a four pin connector like a MOLEX Mini-Fit Jr or regular MOLEX.
In the picture, there is a DB9 connector which is common to many of the MGL modules (specifically the RDAC, servos, AHRS, and compass). My suggestion is to build all of them the same – a DB9 connector with both the male and female MOLEX four pin connectors. Interconnect each module with "extension cords" made of a shielded twisted pair plus red and black 20AWG wires for power and ground.
By building common harnesses and the extension cords, it is easy to add modules to the CAN bus in the future. Connect the standard harness to the new module; temporarily pull out the extension cord, cut it in two and add the corresponding four pin connectors; install the two shorter cords with the new module in the middle. Alternately, if you know you will add a module sometime in the future, just build the two shorter extension cords now and plug them together until the time comes to add the new module.
At the time I was building my CAN bus harnesses for the Mini EFIS, RDAC (engine monitor module), AHRS, and magnetometer, I was expecting to also install the MGL servos for its autopilot. Thus, the long run from the panel to the tail cone – where the magnetometer is traditionally installed – is actually three segments: from the panel to just below the pilot seat (where a roll server would go), then just past the aft baggage compartment floor (where a pitch server would go), and then up to the shelf where the magnetometer is installed. The junctions are just one CAN harness plugged into the next. The idea being that I could just disconnect the two harness runs and plug in the servo pigtail into each end. Since that was a "down the road" plan, I secured the connection between the harnesses by covering them in heat shrink.
Of course, all of the above pre-planning was moot when I decided to stay with TruTrak for the autopilot.