Wires behind the radio were butchered. Most are speaker wires that go to an internal amplifier that needs a voltage to turn on. Gave up and wired around it.

The aftermarket radio does not support picking ip the turn signal from GMLAN.

I bought a PAC LCGM29 but can't find the GMLAN signal. Put an oscilloscope on the various wires. Pink looked promising but didn't work.

 

Pink is the antenna amplifier/ power on signal if you have a sub-woofer.
(there is a link in my sig to free shop manuals)
Here are the diagrams for w/amp and wo/amp:
radio noamp.pdf
radio wamp.pdf
radio connectors.pdf