These manuals (or copies) are available on eBay most all the time.
you don't
1966 GTO
Here are the 66 wiring diagrams: http://www.hammar.dyndns.org/wiring/wiring1966.htm
I restored a 1970 Pontiac Tempest about 15 years ago. I purchased a book that contains very detailed diagrams of every aspect of the car. If you're still looking for a wiring diagram, I can try to dig out this book and find it. (There's no date on this question, so I'm not sure how long ago it was asked)
go to http://www.hammar.dyndns.org/wiring/wiring1966.htm
Be wary of the tempest in a teacup. The tempest blew our ship aground.
I know that this rear is a gm standard 10 bolt, and Pontiac used it in the 64-66 gto, tempest, and le mans.
Tossed by a tempest.
A tempest is a violent storm.
Tom Tempest was born in 1876.
Tempest Storm is 5' 6".