I've got a 87 Diplomat SE that the cruise is not working in. Speedometer works fine so I'm assuming the speed is getting through it and too my speedometer and there is a strong vacuum coming from the power brake booster. Anyone have any tips for troubleshooting these things. I have to admit with all I've done to vehicles I've never had to troubleshoot a cruise control system and I'm a bit stumped as to where to start here. I appears there are only 3 wires going to the unit under the hood. Is it possible to test the vacuum system that holds the throttle?