Dura-Spark II with Dual Mode Timing

Some models have a special electronic control module with a third connector with 3 wires. See Figure. This connector attaches to a special switch. The switch is either a distributor vacuum modulator valve, used on engines with the fuel economy package, or an ignition barometric pressure switch, used on altitude calibration vehicles.

This switch allows base engine timing to be modified to suit either altitude or engine load conditions. All other operating characteristics of the module are the same as for Dura-Spark II systems without the special switch.