[FrescoGreen01.5]

You say the alarm and the windows are working. I assume you have "door open" indication on the dash (instrument cluster)? If you do, then the Comfort Canbus is working, thus the CCM should be activating its output that turns the interior lights on when you open the door.

That output is the blue/gray wire on the 23-position CCM connector, pin 16. The wire changes colors to brown/white in the red 10-position connector at the A-pillar connector station (beside driver's left foot), then goes to the lights (up in the headliner). The CCM connects this wire to ground when the doors are open to make the lights come on.

Since someone made some poor quality repairs, maybe they messed this one up, too. (These wire colors are from the US Bentley manual; they're probably correct, but no guarantee.)

Regarding the fog light: I assume you mean the rear fog light(s)? US Passats don't have rear fogs, and the taillight assemblies are different, so I can't help much with this. But apparently the brake light and fog light circuits are somehow connected together when you plug that connector in, and they shouldn't be.

The brake (and rear fog, AFAIK) circuits don't touch the CCM, though. The CCM is only wired to the turn signal circuits (so it can blink the turn signals when you lock/unlock your doors).

 

[FrescoGreen01.5]

This is a networked system, using Canbus...

There is a Canbus node built in to each door's window motor, one in the CCM, and one in the instrument cluster (plus a few others depending on year and options). (This is the Comfort Canbus, to be distinguished from the powertrain Canbus.)

When you open a door, the microswitch in the door turns the puddle light on directly, and turns on an input to the Canbus node. That door open status is reported over Canbus to the instrument cluster (to turn on the "door open" indication) and the CCM (to turn on the interior lights, among other things). There is no direct electrical connection, just the Canbus network.

That Canbus network is also how the "lock/unlock doors" and "raise/lower windows" signals get between doors and CCM. When you lock/unlock the doors from the keyfob, the keyfob transmits to the CCM, which then sends the lock/unlock signals to each door over Canbus. Thus, that's an easy test to know the Canbus is working. The "door open" indication on the cluster is a good indication, too. It sounds like your Canbus may not be working.

The Canbus is a small-gauge twisted pair of wires (orange/green & orange/brown). It's spliced in the floor harness, since it goes to all four doors, the CCM, and cluster. Since your floor harness has been poorly repaired, I'd look there first. Canbus is pretty forgiving, but do maintain the twist up to any splice, and make the splices cleanly. Crimp butt splices, if crimped with a decent tool, are my preference.