'73 B-body wiring diagram indicated Ignition 2 wire goes from cavity 22 to the the ballast resistor. On the diagram its labeled J3.
There it is crimped to the same terminal as wire (J3A) which goes to the coil positive.

If you still have the original, it could be used.

It should look something like this under the connector at the ballast - except on a '73 the diagram indicates both wires brown (J3 and J3A).
On earlier cars, the wire to the coil is dark blue. I don't which year the color was changed.