I havent done it to a w126, but I have done it to an 81 2d0D, and plenty of W124s.

you will need to wireup relays to activate the central locking on the w124, same should apply to a w126, otherwise you need to put an actuator on the drivers door to pull that lock down which will in turn activate the rest of the vaccum locks.

if you want a wiring diagram which tells you which wires are tobe hooked up to the aftermarket alarm, I can get one. It is not an mb wiring diagram, it would be from audiovox.

Alon

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'92 300CE - Sold
2004 C240 - 744 - C7 Wheels - Android Radio
2002 C320 - 816 - Sport Wagon - Sold
2006 E350 Wagon - 368 - Dead
2015 GL350 Bluetec - 197U