Hello Paul,

It sounds like you are on the right track.

Mercedes fitted an alarm to the Central locking/immobilizer system on this car to up the Thatchams security rating.

The alarm system interrupts the C Can at the central locking unit (IFZ module). This stops the engine starting as it does not see a valid unlock code from the IFZ module even though the correct key was used.This unit is under the drives foot plate next to the alarm box.

On the unit there are 2 connectors, one of them only has 2 wires. These are the C Can wires, Green and green/white. One of these wires will have been cut and the alarm unit joined into the break. All you have to do is re-make the straight through connection to the cut wire.

Please post your findings

Regards

Andrew Ruellan