Stereo in GMC Savana

I am trying to install an aftermarket stereo into my 2008 GMC Savana. I know that there is power going to the new unit but it will not turn on. I tried another stereo I know works, but it to does not turn on either. I know power is getting to this unit as the led in the back lights up. Strange thing is that the light is surging, like the power is fluctuating. When I attach the wires to the old stereo it works just fine. There is one wire I am not sure of however, light green. What am I missing here. It is driving me crazy. Any help to this mystery would be great.

You know you have power.....but what about a good body ground? Takes both power and ground to complete the circuit.. You may be grounding through the speakers without a good body ground.

Oh, the black with white tracer is the ground wire for the OEM radio on your van.

Thanks for the reply. I attached the black wire from the new stereo to the black wire that comes with all of the other wires. Do I need to run a separate ground wire? I do not have the antena hooked up yet as I need to pick up the adapter. Would that be a problem?

It is still not working. What on earth. Any help would be so welcome. Does GM do something that makes you have to buy their equipment.