Trailer wiring
 

I feel like an ass b/c I can't figure this out so I've put my flame suit on and I'm bustin' out a post.

2004 MSM
Curt wiring harness https://www.etrailer.com/Custom-Fit-...id=20041174279

Harbor Freight Trailer: Heavy Duty Utility Trailer - 870 Lb. Capacity

The parking lights work, brake and turn on both sides do not. Added dedicated grounds to the rear lights as suggested by some to solve the issue. Made sure the grounds are not going over paint/powder coating.

Tried following the FM hitch wiring set-up: https://www.flyinmiata.com/support/i...hitch%20NB.pdf

And this wiring set-up: Mostly MIATA: Trailer Hitch Installation

with the same results; power to the parking lights and that is it.

Any ideas what I need to be doing different? Do I need a different wiring adaptor to deal with the independent brake and turn on the Miata vs. them being combined on the trailer?

Thanks.

They should be working if you followed the quoted instructions, i would first see if When you turn the position lights on one or both bulb filaments come on, only one should come on.
Then use a test loght or bolt meter to see if you are getting 12v at the correct converter box wires for turn and brake lights, it seems unlikley that you would have 3 bad tap connections.
If you are getting voltage on each turn signal and brake light coming into the converter box the box is probably bad, if you are not the problem would be bad connections (or a blown fuse if your car lights are nor working either).