Think of electrical current as a water hose.
Valve off (ign sw off), no flow of water (current), max pressure (voltage).
Open valve (ign sw on), water flows (current flows), pressure drops, (voltage drops).
Twelve volts with ign sw on IGN, and if point set is open, or module not working/spinning, max volts and no current flow.
If points are closed, then current flows, as circuit is complete, then lower voltage.
It may be true with yours, but a previously owned '67, needed the yellow wire from R terminal on solenoid to coil + for start voltage.
My previously owned '68's had twelve volts from ign sw START position, but yellow wire was still installed and I left it this way.
Sixty-nine is probably the same.
With nine volts during cranking, either/both, the battery is low charged or too small, and/or battery cables too small of gauge, min of 1 AWG and wire brush posts and clamps and attachment points on block.
My suggestion is externally charge battery overnight. Next day, check voltage on disconnected yellow wire and disconnected cloth covered white wire during cranking. Remember, start motor is a high current device and expect a drop of battery voltage, but not lower than nine volts, typically.
"Need more power, Scotty" comes to mind.
If white wire is 12 volts during cranking, you could, not required to do so, do away with yellow wire, but I would leave it and use it.
When connecting new 8360 distributor, tie back white wire and run a new 12 AWG wire from IGN spade on fuse panel, as this action will leave OE white wire for 480 distributor when installed.
