If it has been rewired without following the original color codes, and especially "...that it had been re-wired ... all wrong....", then I don't think the original wiring schematic will help you very much.

However, I do have the Volvo (factory) "green" service manual for the 1975 164, and I can scan and e-mail the wiring schematic to you -- it's from pp 3-55, a multipage foldout from the manual. I'll have to scan it in two parts (the whole thing won't fit on my scanner), and you'll have tape it together into a complete large sheet. Give me your e-mail address.

P.S. -- if anyone else would like to see it, too, let me know.