Wiring is very confusing for me (or at least the original Chevrolet diagrams are very confusing to me), but I believe the front harness bulkhead connector was keyed for both with and without gauges, but depending on what the car came with (idiot lights or guages) was where the change was made. In this case, the bulkhead connector for the idiot lights or the amp gauge entered the car at location "BS" for both, and was a 14 gauge Black/White wire.
If the car came with the Amp gauge, the fuse panel continued with the 14 gauge Black/White wire going to one side of the amp gauge, then back to the fuse panel from the other side of the Amp gauge with a 14 gauge Black wire that went to location "AS" on the bulkhead connector, then finally back to the junction block.
Idiot light cars also had the 14 gauge Black/White wire at location "BS" on the bulkhead connector, but this turned into a 16 gauge Brown wire out of the fuse box that went to the Generator light (and a 24 gauge Brown/White going to the ignition switch).
It's all very confusing, but I believe the 14 guage Black/White wire coming from the 20 guage Orange fusible link was used no matter if you had idiot lights or guages. The change was made inside the car at the fuse panel.