Quote Originally Posted by PlayingWithTBI View Post
I honestly don't remember any small ground wires going to the back of the engine, only the ground strap that goes from the head to the fire wall. As @Dieselsj said I found both the black/white and tan wires double crimped to the eye on the T-Stat housing. Maybe GM changed its location later on?
It is possible. I'm used to seeing a dedicated ground. Perhaps GM initially tied it in with the other grounds, then later switched to giving it it's own grounding point. Any difference of potential or noise here would reek havoc on the O2 signal. Eventually GM, and everyone else, switched to 4 wire O2 sensors to ensure a good sensor reference.