Six pin switch for non factory air conditioned cars. 

VERY EXPENSIVE switch & lock matching.. but it is 6 PIN.. .. hard to get.. hard to justify..  NOS costs more then US$200 trending around mid 2015.. 

No Longer made by GM..

(Not to be confused with the ignition barrel and lock or a 5 pin one for other GM vehicles of the same era.)

This section is the part behind the barrel you see only when you stick your noggen up behind the dash... the LOCK goes into this.

Normally ONE set up in stock..