OK, here's the quick summary of problems with my 2000 convertible:
1. Grinding sound in left headlight... replaced the stripped plastic gear with a brass one from Rodney Dickman. Worked perfectly, until...
2. About a week later, I turned the lights on and then back off again. The left light went down and then popped back up about halfway. Someone on the forums alerted me to a TSB to fix this exact problem... ordered the parts cited in the TSB.
3. Received the parts and installed three washers and two new insulators per the TSB. Worked perfectly, until...
4. About two weeks went by when I jumped into my car to go someplace and my headlights both came up since it is dark in my garage. Out in the sunshine, they both dropped down (Twilight Sentinel) but the left one popped right back up again just as it had done before the TSB "fix". The headlight is off but the headlight door is open about halfway.

I have also tried (as was suggested on another thread) unplugging the headlight for several minutes at a time and then replugging... did that several times, in fact. Nothing seems to fix the problem permanently. This headlight seems to have a mind of its own. What's the next thing to try? Exorcism?

 

Grounds, check the grounds these cars love to be grounded.

 

Sorry I can't remember who posted but heres something that may help:

First thing to check is the Headlight Actuator CONTROL module located under the passenger headlight on the front of the passenger wheel well wall. It translates the ON/OFF signal from the headlight switch/BCM to a RAISE/LOWER signal to the headlight doors. The fact that one headlight stayed up during the process indicates to me it's not the switch.

Here's how the control module works. If you look at the headlight connector just behind each headlight (5 wires total). 2 are for Headlight Open/Close, 1 is for Low Beam, 1 is for High Beam and 1 is Ground for Low/High.

The 2 Open/Close wires are Lt Blue/Dk Blue for the Passenger Side, and Lt Green/Dk Green for the Driver's side.

Take the Driver's side for example, both the Lt Green and Dark Green wires always have +12V in steady state. If you have a DVMM, verify that both these wires are providing +12V even with the car OFF. Sicne they're both at +12V, the motor has a net voltage of 0V across it so it stays where it is.

To Open the headlight, the Dk Green is momentarily grounded by the control module (i.e. +12V on the Light Green, Grnd on the Dk Green). Conversely to close the headlight, the Lt Green is momentarily grounded. It appears that the control module was not doing that either because it's faulty OR posibly the connector could be having problems. The first thing to do is try to access the control module and remove/reseat the connectors (there are 2 connectors, one on each side of it). You may be able to squeeze your hand under the passenger headlight when it's up but it's tight

 

Thanks. I will try to run down these leads. I appreciate the advice!