Hi,

The black wire at the #8 pin is a ground for the control unit. It goes from the unit to somewhere on the body of the car. On my 91 I traced it to the left side of the center console. On a 92 it ended up on the floor by the passenger's left foot. I don't know about your 93.

If you have a meter, you could disconnect the plug at the control unit and check for continuity between that black wire on the harness and any ground point.

The VSS is the vehicle speed signal. It comes from the rear axel to the speedometer. A functioning speedo would indicate that part is alright.

That signal is then sent to the cruise control unit on a yellow wire. A 90 would get it from the double spade. Later models get it somehow from the blue/black wire at #6 on the big plug at the back of the gauge cluster. The Bentley schematics simply show a yellow wire between the speedo and #5 at the control unit without any details on how it gets there.

The brake lights are also part of the circuitry. They have to be working normally for the cruise to work.

I haven't looked but there's probably information in the FAQ about testing the stalk or other components.

Peter