Transmission gremlin

Hi, I've been experiencing transmission problems on my 2002 CLK 320. The care has 180,000 miles with a large % of those miles on the interstate between Phoenix and Tucson. Codes came up regarding the 2-3 shift solenoid. I had all of the electronic components replaced except for the control unit. Transmission fluid was pretty clean, Adaptation values were at the highest 50 (top end spec is 180 I believe), no signs of transmission issues outside of the electronics. The symptoms both before and after this servicing, when my 100 lbs teenage daughter drives the car and I am in the passenger seat (I weigh 200 lbs) it will not come out of first gear. No problem when I drive the car with a light weight passenger. When I drive with a 200 lbs passenger the same problem occurs. Usually, I can restart the car and as long as there is a light weight passenger there is no problem. Question: how do I indentify teh weight sensor plug under the seat? I want to unplug it and see if the problem goes away. Is it the yellow plug? Thanks