Duke Hamilton 1999 E 46 writes:
In my E46 Pin 10 is empty on both plugs both the factory harness and the TP Adapter. So adding the plug you are talking about would buy me nothing if I am just doing it to include the black and while wire into the cluster since it would be connected to nothing on the other side???? ...
George explains:
Your E46 appears not to have a SSV/GAL going to the head unit.
Maybe E46s don't have SSV. Since most of us are Z3/E36ers,
hopefully another E46 person will step in here. But you do not want
to ground the GAL/SSV, it absolutely needs a live signal. If #10 in
your BMW side harness is empty on both sides (female and male), then
your gut is right to fell something is off base. The person below
was telling you to ground your back-up lite, which was
blue/greenish/yellow (which I actually tapped into the back-up lite
w/). Looks like your going to have to find it in the dash and tap
it. I am very sure the TP will need the GAL to operate correctly.
Duke answers:
Found it in the glove box...

Adam writes: My troubles trying to install the TP in my E46: I had
never heard of ISO mounts before I tried to install the TP and was
under the assumption that DIN was the universal standard. The
installation kits from Scosche, American International, etc. all
fit the E46 with aftermarket DIN head units. Therefore, I thought
that since the TP is DIN sized and these trim kits support DIN
units, I would be fine with getting one of these cheap $20 plastic
things, instead of having to wait for BMWs version to come off
back order or get a custom piece done. However, what they do not
tell you are that these aftermarket kits only support ISO mounts.
This usually is not a problem since most head units are Japanese
and, as the article states, are all ISO compatible, which means
that the unit sits completely behind the mounting device and the
front of the unit is basically the same size as the back of the
unit. However, this is impossible with the TP because of the big
plastic trim that surrounds the front of the unit makes it way to
big to accept an ISO mount .