The cruise control amplifier can be removed w/o affecting the driveability of your car. I would also not rule out the actuator. This is located on the driver side of the block below the intake manifold. "Cold soldered" joints are not always easily visible to the naked eye. Look for signs of corrosion, or "tracking", or any obvious breaks in the conductive traces on the PC board. The actuator hangs out in the weather, and can be the victim of excessive engine washing or moisture. From what I have seen here, it seems the amplifier is the most common component to fail. Do a search, you'll find a number of posts about this system. Good Luck..
1987 BMW 325