[Qmulus]

While you had power to the alternator, did you have the 2.5mm red wire along with the large cable that goes to the connecting point, and was it intact? You should check continuity between there and X59 (white connector) pin 14. On the other side of the connector it goes to a 4mm wire (because the Maxi fuse terminals are only available for that size) to the fuse holder. Like I said, in most cases you will find the breaks at the ends. That said, also check for chafed or pinched spots in the harness, or melted spots. I still will bet on the ends, either at the alternator, large multi-pin white connector in the back (check both sides of the connectors). or fuse holder (check from behind).

The ONLY thing that wire powers is the secondary air pump, so it is no surprise that everything else works.

Honestly, I haven't bothered to rebuild these pumps in a couple of years. If you want a core, I have a big box of them. For a while you could get new ones for less than $100, so it didn't make sense to rebuild them. That and people were throwing pumps at cars with leaking combi valves that killed pumps in a matter of weeks by filling them with exhaust vapors and expected warranties for that. I had made a prototype replacement with a brushless motor that eliminated the issues, but I lost interest in that project.