Hi, I am in the process of fitting a non-original cruise control to my '88 250 Turbodiesel wagon. I had this particular unit installed in a w123 and it worked great - however, the back of the speedo is different on the w124, and there is already a sensor fitted.

This little devil goes by the name of VDO 007 542 29 17 and has a + and a - marking on two of its three connectors. The last, much fatter one does not have any markings - is this the one to use for the lone wire from my unit (the w123 required only the one wire and a chassis connection)...?
Any help would be appreciated!

Kind regards from overseas...