Retro, I am working on getting this info, and you are going to shit when you find out where I am getting it from.
Here is some starters, you may be able to guess who it is, lol:
I'm into the 03 T&C as we speak. I'll get you what I have available.
Automatic Headlamp System This feature is available on vehicles equipped with both the Electrocromatic Mirror (ECM) and the Compass/Mini-Trip Computer (CMTC) .
The Automatic Headlamp system turns the instrumentation and exterior illumination lamps ON when the ambient light levels are Night and the engine speed is 450 rpm or above, and OFF when light levels are Day.
Automatic headlamps are controlled by the Body Control Module (BCM). With the headlamp switch in the AUTO position, the BCM will control the headlamp, parking, side marker, tail and instrumentation lamps based on ambient light levels. Ambient light levels are monitored by the BCM using the Day/Night signal and Electrochromatic Mirror (ECM) present from the Compass Mini Trip (CMTC) located on the front windshield in front of the rear view mirror ECM. Ambient light readings are averaged to limit cycling the lamps ON and OFF when passing through areas with varying light levels. The automatic headlamps will only function when the engine is running with RPM> 450. When the headlamp switch is in the AUTO position (Automatic mode), the Headlamp Time Delay system will function when the ignition switch is placed in any position other than run/start.
COMPASS/MINI-TRIP COMPUTER Compass Mini-Trip Computer (CMTC) and Compass Temperature (CT) data is obtained from the Body Control Module (BCM) on the J1850 Data Bus circuit. The CMTC and CT will display dashes (- -) for any of the screens it did not receive the bus messages. The label corresponding to the missing information will be lit. If no compass mini-trip computer data is displayed, check the J1850 Data Bus circuit communications and the BCM. If the brightness level is improper check the J1850 Data Bus circuit.
The DRB III is recommended for checking the J1850 Data Bus circuit and the BCM. Perform the CMTC, CT self diagnosis before replacing the CMTC or CT module.
It might be easier if you describe the problem with the auto headlights.
Here is a good look at how the auto-dimming mirror is wired. A photo cell (not shown) sends a signal to the BCM which in turn sends it over to the mirror. It also appears that the back-up lights (car is in reverse) are somehow involved: