Is it the same system as the RRC of thatyear? if so the first thing to check is the condition of all the vacuum hoses, partuculary the ones at the back of the engine near the vac actuator on the throttle linkage. They perish and split with annoying regularity.
Another problem is the rotary connector, it can go open circuit and as a failsafe all the switches need to stay closed circuit other than the set switch.
