70 up charging system upgrade question

If the black one is in good shape and fits the switch the fact that it has a retainer is "some points." But really that should not affect electrical.

Since you have the ign switch right there I'd check right there for drop

If it's easier to understand, "rig" an extension wire to the battery NEG. With the key in "run" and again in "start" check the following::

The backside of the connector check battery coming in with key in "run." If this is close to battery, it is OK. If it is low, you have a drop between there and the battery, IE the RED wire in the bulkhead, or the ammeter

Next check the "run" (BLUE) and see how it compares to the battery coming in. If it is quite low at the BLUE compared to the battery supply, then you have a drop right there in the connector or switch

Same thing with IGN2. Again, make these checks with wiring all hooked up ready to run. You can ground the coil high tension for safety if you feel the need.