Mariner Navigation Unit
 

Note- all parts mentioned are Ford OEM products (no aftermarket items). Just replaced my stock Ford stereo unit (BL8T-19C157-BA) with a Ford Nav Unit (BL8T-18K931-BB). Installation was quite straightforward. Connections from the old unit fit right into the new unit, except the was one small four pin connection from the old unit that didn't have a place in the new unit. This connection came from the upper right side of the face plate. Trying to find a manual or something to tell me what it is used for, so I left it hanging. Had a small issue with the GPS antenna. It didn't like being inside the dash area. Had to put it on top of the dash before it would get a signal. Well, when I tuned on the unit, everything seemed to work fine. Got a GPS signal, set the clock, paired the phone, radio station signals were OK. Big issue was no sound, except when I turned the volume to the max then I could just barely hear. Any thoughts out there (before I take it in to a dealer)? Thanks.