Well it seems the cluster and harness are out of the car together ( I can see the firewall hole for the bulkhead ), while parallel paths are still on car since they didn't get a quick disconect plug, and still on firewall on that visible grommet.

The black wire can't be disconected from amm post since the ammeter post needs to be used as juntion to get together the parallel path and the main splice to be sourced from alt. Diff story is to know what we do have on engine bay side, if stock alt wire is being used or not.

if ( same as the red one ) is not being used, better remove it to not keep a hot wire hanging around. On red wire case, just remove the 16 gauge fuse link is enough.

if bulkhead paths are still healthy on both, red and black, I DON'T SEE a reason to remove them. I'll keep using those. BUT once again, just using ONE fuse link... the 14 gauge one, so both reds spliced into just one fuse link.

My 74 got the AC harness running out of the bulkhead and is on that way from factory in every 74 with AC due the lack of cavities left on bulkhead once the interlock starting system bypass was added. So ON MY CAR I used this same grommet to run together the AC harness and parallel charging paths, just enlarging the AC grommet hole to fit all 4 wires through the rubber. I didn't want to cut my firewall for this just to run couple of wires whcih are not stock. If this car got factory AC ( which is my understanding ) the parallel paths are running throught that same factory AC harness grommet, just AC harness is not there. I think to recall the AC harness grommet is located just right there like the one shown on pic

In 74 the tach when optioned run by the ONLY cavity left by that year on bulkhead at NSS plug section

In previous years, the AC harness used the blower source ( also for heater ) at the only NSS cavity left and the compressor clutch at the only engine harness cavity left, while as far I recall tach run with a grommet... so it was reversed than 74s