Resolved 2G Low voltage from alternator/battery

[b00stedAWD]

Few months ago, I recently relocated my battery to the rear. Everything was ok until past three weeks when my battery voltage started dropping. I'm using 4gauge wire from alternator to main fuse box and 0gauge from fuse box to the battery. Alternator is 150amp, battery is Optima redtop.
Using DMM, car off the voltage is 12.4-12.7 on battery, alternator fuse, and the B terminal of the alternator. I did the same test with the car started. Readings were same 12.3-12.7. So I replace the battery to see if it changes anything and no the outcome was the same. I then replaced the alternator and it still reads same volts. Took the alternators and the batteries to a local auto store for a test and they all tested great. 14.8-14.9v was pushing out from alternators during bench test.
I'm at a loss. Only thing I haven't checked is my Harmonic balancer to see if it split. Like I had mentioned above, everything was fine until three weeks ago. Any input is appreciated.

 

[luv2rallye]

I have to finish reading thru the post to see what went wrong and what I will be looking to replace or fix but for now I have power hopefully this will not harm my ECU.

Probably the alt's red Sense wire which goes to battery + was broken.

 

[KingDC]

Probably the alt's red Sense wire which goes to battery + was broken.

Im not sure but for now everything is working so hopefully i can keep it smooth until such time that im replacing ecu and or harness

 

[KingDC]

Probably the alt's red Sense wire which goes to battery + was broken.

It’s been a few days no issues. I do notice the cluster lights pulse slightly when I use my indicators I wanna try updating my grounds hopefully that will improve things