Checked the glow plug relay and it seems to be fine.
Installed the new voltage regulator, battery reads 12.5 off, 13.5 running, when I introduce load (lights and fan) it drops down to about 12.5 and doesn't seem to recover.
Could this be because the brushes on the new Voltage Regulator are new and not yet curved to the commutator in the alternator, or do I still have a faulty alternator? Thanks.