I added a jumper ground from the body of the alternator to the negative it the battery. I'm holding steady at 13.4 volts. I'm about 5 minutes of idle right now with occasional revving to about 1500. Jumps up to 13.7, dips to about 13.2 then back to 13.4. Just a bad ground?
now you are getting somewhere grashopper. you have to eliminate all those variances. test ALT <> GND, engine <>GND, frame, body, etc., etc.
you want no lossses.
same with the hot side. no losses. if you find a loss, repair or replace that segment. you can get away with .02 loss thru the whole thing either side - or + - ..more than that .02 you got an issue somewhere.