Just to clarify, I have an 06 hhr with base stereo and no onstar. I can just use the cheap harness that's not gmoslan if I don't care about the turnsignal or warning chimes? Thanks in advance.

 

Sounds right to me.

 

You could, but why not do it the "right way" to keep all of your HHR's functions intact, you might miss the chimes in a case of forgetting to shut off your lights/leaving the key in the ignition/etc.

Shop around for the correct harness, including a check on e-bay.