I had a viper 330 installed in my 1990 300E. It has extra channels as well and I enabled the auto window down module to raise/ lower windows via the remote, and you can also do an auto starter. In its basic form it provides the keyless entry you need.

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Chris Singh
1983 300D
1990 300E Black Pearl Monotone w/ chrome AMG monoblock II 17", custom multimedia system

1993 500SEL brilliant silver w/ AMG monoblock II 19"

http://benz.mp3car.com
http://stormworks.max3d.com