We have a '93 300TE 4Matic. The 4Matic automatically engages everytime you start up the car, the light does not come on, at about 12mph it shuts down and the car has normal 2 rear wheel drive. While driving if you hit a slippery section of road, large rain puddle or icy spot the 4Matic will engage to control the traction. On totally slippery surfaces the 4Matic engages through three progressive degrees depending on traction.

If you shut the system down with the switch under the hood you not only lose the rear support system but you lose the traction control you might need on a summer rainy day. With the system engaged you are only using it for the short period of time each time you put the car in motion. I don't think that's a good trade-off. We leave ours engaged all the time. We have had very minor repairs to our 4Matic system in 260M miles using it full time.

srharvey
'82 SL 160M
'83 240D 240M
'93 300TE 4Matic 260M