VR Voltage problem

[westerlybreeze]

Hi, just want to get your thoughts as to what could be causing low voltage to my accessory circuit.
Head lights are dim but occasionally come right for a couple of seconds, fan and cigarette lighter
socket very low as well.
Engine loom is VR, but rewired for Ecotec block. What happens if the two wires (not main battery cable) to alternator are swapped from pin to pin?