I have a 2015 MKZ and about a year ago I upgraded my Sync 2 to Sync 3. I have been reading this topic and others like it for the last couple of months and decided to try my hand at upgrading the modem to 4g.
Well, today I did it, and although there were some things I couldn't figure out I got through it without bricking the modem or my car.
I couldn't find a Hj5t-14g087-uf modem at a reasonable price so I decided to give it a go with a jl3t-14g087-cf.
So Start Stop Lock and Unlock work and it monitors fuel level, oil life and tire inflation.
I couldn't figure out how to monitor the TCU to see signal strength and the status of the module among other things
Also, I saw images that in addition to start and lock and unlock also had lights and horns.I don't have those.
I also saw it mentioned that you had to plug in your old antennae cable as well as the $g cable but my old cable didn't fit on the tan connection so I only have the 4g antenna attached to the purple connection on the modem.
I do have a GPS antenna that was installed in the front of the car when I upgraded Sync.
Anyway, I am excited it worked and want to thank each one who spent their time sharing info and instructions so that those of us with no clue could make this happen.
Thanks so much and enjoy your holidays