I recently had my alternator changed but I still have the issue of the battery light coming on at high revs. I told the electrical techs who took the codes and said they would replace the already replaced alternator free of charge. I suppose that's OK - i won't look a free gift horse in the mouth - but i don't think it's the alternator at fault. I suspect the negative battery cable.
I tested the cable temps but they were not much above ambient. Notwithstanding this I still suspect the negative cable:
Reason, When my battery light was coming on a couple of years ago I tested the battery cable temps and the positive one was running hot. I subsequently changed the positive battery cable (but not the negative) and all was good up to a couple of months ago. Even though the negative cable is not getting much hotter than ambient I still suspect it because -
1 it was not changed,
2 the fault is infrequent suggesting if there is resistance it is only small. That would concur with my theory that the negative cable is bad because of the finicky nature of the electrics whereby one can expect even a small resistance out of spec to cause issues.

The upshot of all this is I have sourced a replacement negative cable and will have the techs fit it when they do my free alternator change. Hopefully that will put the battery light issue to bed....
Thanks to Thermo for his diagnostic advice previously.

 

Clack, a trick you can try is getting a decent gauge wire (say a 10 gauge wire) and tie one end to a ground point and let the other end get up to the battery. You can then press the wire against the negative battery terminal (the lead part, not the metal band around it). if you can see sparks come off as you touch it, bang, proof your negative wire has a problem. In this case, you need to look at the whole wire, not just the terminal end. It is possible you may hsve a high resistance where the cable attaches to say the body or the engine block. This is where when fitting the new cable, you want ot make sure that the surfaces where the new cable are touching is clean and rust free.