Used D3 install in a 2003 GMC 2500HD

[jgmeess]

Just installed a used d3 today. Having an problem with ill wire. Tried all three spots. The orange on the onstar box the the orange with black stripe and nothing. Then did some internet reserch. The put it on the light switch. Same thing nothing. With the radio on and I unplug the ill wire it goes brighter. I'm lost. Last thing I noticed that is way wrong. When I turn the key on acc. the radio turns on(good) but it is also turning on my dash lights(not good). I guess this would explain why the screen is dim.(until I unhook wire from switch). So any help would be great.