Keyless entry early W126 - illustrated
I completed the job this weekend.
While my experiences will help you avoid errors in the factory documentation, it's still a long, involved project and not for the faint of heart.
In addition to keyless entry, this installation provides an in-cabin diode, flashing lights and honking horns and a panic alarm.
The like system on my 1990 560SEL (albeit with completely different wiring) has performed flawlessly for 2 years now.
The Omega Crime Guard REC-11 is available from Crutchfield.com. The three SPDT relays can bought at any better automotive or electronics store. $100 in parts, $$$$ in labor.
My tests indicate a 47 yard range from behind the car - the antenna is buried under the steering column, so that's quite exceptional sensitivity. By contrast, the late W126 installlation on my 560SEL, where the antenna protrudes under the rear of the car, has a range >80 yards!
Go to my web site - Cars - Technical - Chassi - Keyless Entry Early W126.