Barometric Pressure Switch: Description and Operation

Fig. 19 Ignition barometric pressure switch. 1984-87:

1984---87
This switch, Fig. 19, controls spark timing and/or other electrical devices according to barometric pressure changes. Calibration resistors in the switch assembly cause the ignition module to vary the spark timing. Spark timing is advanced for vehicle operation above a predetermined altitude and retarded for vehicle operation below a predetermined altitude. Some switch assemblies control both spark timing and another device while other switch assemblies control only one or the other.