I pulled a number of 199x cruise controllers from 190E ( gasser ) in the junk yard and they work perfectly in my 190D, 87 300D and 300SDL. The controller is easy to get to, underneath the passenger side carpet. It seems the controller plug at the top of the controller also does not matter. Have not tried the w123 300D as it is in NoCal.

Hope this info is useful. Disclaimer: it works for me but every car is different.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

I've done the same. The big difference in the coding plugs is how it locks the desired speed. The one I'm using now in my '85 190D, is from a '93 190E. When you are traveling at, say, 70mph and 'lock' the speed, it isn't smooth. The speed increases a couple of mph. The reverse is true for others. The one I have now is a compromise and the best I found out of several I tried.

I had the proper coding pug on the unit at one time but it failed very shortly after I installed it. When you have the right one, the transitions are smooth. You lock a speed and it stays there without perceptible change. The plug for my car is no longer available. It wasn't worth the postage to send for repair to James Dean, one of our posters.