MTX-L GND or SG?
 

I'm still trying to find the perfect match between my DIYPNP, MTX-L and Tunerstudio. Currently I have the wiring for the wideband going through the DB15 connection, with 12V to pin 1, O2 signal to pin 4. The MTX-L only has one ground wire serving as both power ground and signal ground as I understand it, so would it make much difference whether the ground is wired to GND or SG on the main board?

Use GND, not SG.

Got it, thanks.

Make sure you have a fuse on that 12V feed. You wouldn't want any potential problems with the wideband to disable your damage your ECU.

Is there a particular amperage fuse recommended, or is a standard 10 amp inline ok?

I'd use a 5 amp fuse.