I choose to use Tezfel wiring throughout my plane. Yes, you can use other types of wiring, but there are good reasons why there are standards for the wiring that goes into certified aircraft.
How often do you think you will need to remove the wings? After lots of thought and advice I decided not to put connectors at the wing root. Every connector is a potential source for problems (poor connections, corrosion, etc.) and EMF (noise) if it is a shielded wire. I have lots of experience finding corrosion in connectors, including wing root connectors. I really didn't want to put a connector in the magnetometer wiring, it is a very sensitive sensor. I made my wing wiring so it could easily be disconnected and pulled out of from the spar tubes if ever need be. It would only take a few minutes to do this after opening the wingtips. I bet it will take far less time to do this than to troubleshoot and repair a problem in the wing root connectors.
Per the Garmin criteria there isn't a good place to put the magnetometer in the entire plane. I ended up mounting mine on the outboard rib of my left wing. I used shielded wiring for the nav, strobes and landing lights and all of their grounds returned in the same wire so that there would be minimal EMF. I also used stainless steel screws for my wingtips (certified planes use brass or SS).
Don't use the spar or airframe as the ground as it could lead to EMF that could affect the magnetometer. Doing so can turn the spar or airframe into on big EMF antenna.
The G3X will self test for problems with the magnetometer; they have you turn on circuits one by one while the unit is checking for interference (it is pass or fail). Initially mine failed when the landing lights were turned on and I had to reposition the wingtip connection farther away from he magnetometer, then it was fine.