High Voltage

16 ga is plenty large enough for the blue wiring. It would be nice to see less drop, but that drop is not all that bad. But, you need to measure these voltages at fast idle; if the 15.3 volts is a regular low idle, then the VR is not doing its job. I am suspecting that the VR is not operating at the proper set point. How is the grounding to the VR? A good bare metal contact? And the battery ground to engine and chassis? You can measure between the battery - and the VR case to be sure that is almost 0.0 volts.

And is this VR a non-brand name unit? I was working with another fellow recently who went through 2 chain store brand VR's, and everything became good when he put in a new Wells VR.

And I don't want to waste your time but measuring the voltage drops from the VR back to the battery would be a good idea, just to be sure it is not unusually high at one point.

And this is not necessarily and issue at this time but.... What type of fuse and fuse holder are you using? If it is a standard blade type automotive fuse, the holders are not rated at more than 30A and you will likely have problems with that over the long term.