Yes, it will reduce the firing voltage of the spark plugs to the point you'll get terrible performance under load, a chronic miss, and really lousy gas mileage. If you want to see whether you've got the right voltage to the coil, check the (+) terminal of the coil with the engine running. With a charging system voltage of 14 Volts, the voltage at the coil should be 9.5 to 10 volts. The whole idea behind the reduced ignition primary voltage is to prevent burning the points during normal running, yet allow the coil to fire at full efficiency during starting by bypassing the ballast resistor when the battery voltage is in the 9-10 volt range while the starter is running. If the primary voltage is reduced too much for normal running, the engine simply won't start due to low firing voltage. The same holds true for a 6 Volt system with dirty connections at the coil or the distributor. Plenty of cranking speed, but no fire.
Jerry
