Ignition switch connection

The '72 Plymouth manual will be very close for almost everything.
MyMopar - Mopar Forums & Information - Service Manuals
And check for TSBs at
The 1970 Hamtramck Registry "1972 Dodge TSBs" Page

3406pk said

I found that the voltage to coil and resistor was lower than battery by 1.5 to 2 volts.

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Is this drop in voltage based on direct measurement? That is, one lead on the battery positive and the other on the connector at the coil with the key in start?