I'm not sure where the tach wire fits in this story but the HEI distributor doesn't use a dropping resistor. That is only for the breaker point distributor. GM began using the HEI system around 1976 so that's what came in your car. All it needs to work is a single 12 volt feed wire from the ignition switch.
These systems were capable of developing 40,000 volts which is considerably more than is needed. All ignition systems only develop the voltage needed to make a spark jump the gap on the spark plug. Once that occurs there is no way any higher voltage can be developed. What you gain with a 50kv ignition coil is capacity to develop a higher voltage. That comes into play, and you have to be careful, when removing a spark plug wire to check for spark. With all other ignition systems if the plug wire is pulled too far away, no spark will occur. With even the standard HEI system, the potential voltage is so high, the spark WILL find a path to ground somewhere. Usually that is through the rotor to the distributor shaft. Once that happens, (called "punch through"), you'll have a no-start condition until the shorted rotor is replaced. A lot of mechanics got caught by that in the '70s when these systems first showed up. Today we fix the distributors all the time, but the engineers at GM never intended that at first. They intended unit replacement, especially since the mechanics didn't understand how they worked at first. For that reason they just knew a new distributor solved the no-start, but they didn't know why.
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Sunday, June 8th, 2014 AT 8:04 PM
