4matic Fault

Help: Have Just Had The Tranmission Rebuilt Fo A 1988, 300te. Now At Idle The "4matic" Light Flashes. Also Noted Is That When The Light Is Flashing The High Pressurre Feed From The Engine Pump Is Loading Then Releasing Via The By Pass Solenoid Near The Rear Fuel Tank.
If You Drive Off Quickly In Say Metal Or Slipperry Conditions You Can Make The Rear Wheels Skid As The Lock-up Does Not Work. If You Take Off Slowly Up To About 5km/h The 4matic Light Goes Out And You Cannot Skid The Wheels As It Has Locked In. When You Come To A Stop The Light Starts Flashing Again. If The Foot Brake Is Applied At Idle The Light Goes Out . Have Replaced The Brake Light Switch. No Change.
Any Cures Please.