The vacuum switch is for the CAD on your front axle. Pull the vacuum lines for it, plug the ends, and lock the CAD over.
Simple write-up for that is here.
On the later 231s (91+), the electric connection isn't for the CAD, as it was done away with. It's for the speedometer. 84-90 was cable driven, 91+ is electronic. The early electric senders simply screwed on where the cable goes, and converted it to an electric signal. The part that holds the speedo gear is the same.