Got a bit of a power problem that seems like it's been getting worse. On a cold start, with no accessories on, the volt meter will read a bit above 13V for a few minutes until the car warms up and it drops to about 13V. I have checked with a multimeter and it reads like 13.4V between the jump start post and ground (intake manifold).
As I add accessories, normally only A/C and headlamps, and the engine is hot, my gauge reads very low at idle (battery light not on though) and with a meter I am seeing only about 12.3V. This has actually been going on for a while but seems worse than usual tonight.
I have an Interstate battery (less than a year old and it hasn't been found dead yet since I installed it), new DPI alternator kit (installed a month ago), the alternator is also grounded to a valve cover bolt, my battery connections are clean and tight, my battery light in the dash (regular bulb) lights up when I put the key in position II, and I replaced the three brown wires between the alternator and starter with a 4 awg welding cable and pneumatic crimped copper terminals. The ground on the trailing arm was also very recently cleaned and reinstalled with all new hardware when I did a full suspension rebuild last fall. I've also cleaned the grounds on the front frame extension and the one that goes to the frame under the header bottle.
I had a Hervey CS130 D120 alternator prior to this new alternator and it did pretty much the same thing.
New Gates 7495XL belt and it feels "fairly" tight. I might be able to crank it a tiny bit tighter but I really don't think it's slipping.
As a test, I also took the single-wire plug off the alternator and started the car just to see what would happen and the battery gauge read even lower and my binnacle (LED) lights started flickering so I know the plug isn't periodically losing connection or else I'd see that happening sometimes.
Any great ideas? I'd love to get this finally fixed.
Here's my gauge at night with fans roaring, A/C on, and headlights on:
PXL_20220626_041946586.jpg