Ok Dave -

The Volvo electrical system is unlike a John Deere, but the physical principles are the same.

Haynes is OK, Bentley is better, the very best are the Volvo "Green" Service Manuals. Go to www.volvotechinfo.com, or call 1-800-25-VOLVO and get the one for your car for Wiring Diagrams. The other books use copies from this one.
Not inexpensive, but well worth the money. I have worn out several.

Wiring harnesses cannot be evaluated from the outside. Go with the one from Dave Barton (guy in California, I presume) and be comfy that you got the right one and a good one. My first encounter with the problem was years back, pre-BB. Dealer quote (in 1995) was $350 for the part and $600 labor. urk urk gag.

Get an alternator at a junk yard. Usually guaranteed to work. Pull and check the the brushes/regulator unit on the JY one and your old one - brushes under 5mm = bad. If you mist, get a new set FCP or another place, $80 or less. Remember that the corner parts house wants to sell you something, puts a bias into their oft-inaccurate test process.

Good Luck,

Bob

:>)