Just finished replacing my alternator belts that broke last week. I too saw the christmas tree lights, but it was just cause the belts broke, not cause the alternator itself was bad.

Fan bolts (4) 10mm, though if there is no belt on the water pump you may have to hold one nut steady while cracking the adjacent one, as the water pump will want to turn with the fan.
alternator mounting bolts 13mm
there may be a nut holding the mounting bolts in, if so that nut is 12mm. on the a/c compressor (I had to take off the a/c belt to get the alt belts on) there were 2 13mm mounting bolts with 12mm nuts.

if i were you i would just get a combination wrench set with all metric sizes from 10mm all the way to 16mm. those are the most common and it will come in handier than you could imagine.

also, the nuts on the fan are righty-tighty, lefty-loosey, not reversed.

hope this helps.
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Nik :: 1989 Tinted Silver 244 AW70:: Chicago, IL :: 153K as of 8/2007 :: Pics and Notes