Yes, that's it. It reduces the voltage applied to the coil primary to about 9 volts during normal running. Be sure to check the voltage with the points closed if you do it with the engine not running, otherwise it will read 12, not 9. The best bet is to check voltage at the coil + terminal with the engine running. It should read 8 to 9 volts if everything is working right. During cranking, there is a bypass circuit from the starter that applies full battery voltage to the coil. That voltage just happens to be around 9.5-10 volts because of the starter load.
Jerry
