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I'm not really sure... It used to work and then all of a sudden stopped working a while ago. I have replaced the amplifier and that didn't do anything and the vac lines are good so now I'm not sure. I don't know how to test the servo or the wiring or the speed sensor to know if I have a bad wire or a component went bad. Any advice is appreciated.
A '79 shop manual would probably be your best bet, unless cruise control is covered in some sort of separate service bulletin (which would surprise me).