I am having a hard time finding my problem... I put a new alternator in my 81 300sd and had battery tested as good (its only 9 months old)

... my battery light keeps coming on at idle and im only seeing 9 volts coming from my alternator with AC and lights and radio fully on at idle @700rpms

WIth my ac off the battery light and brake light and light in the middle of those two(circle with lines around it) stays on...

multimeter from positive on alternater to ground says 9volts

mulitimeter from battery terminals while running say 15.4 volts

battery when turned off says 14.2 volts

blue wire seems to be on tight but i was thinking this could be whats wrong... is there a procedure for testing this wire..

i tried to unplug glow plug relay and noticed that my electric fan speeds up and when plugged back in slows down.. i also seem to think my fan is not shutting off at all... just stays on all the time but the temperature is 90 today...

Any thing im missing or suggestions... the belts are tights and i checked everything i could..