2006 gmc crew cab electical issues
 

Hey i just bought an 06 gmc 1500 crew cab with vortec max package. Its got some wierd electrical issues. Lights flickering, truck not shutting off when key is off, windows not working from drivers control. Gauges going nuts. Ive cleaned every ground and had a spare main ground from battery to engine block. Mine was green and nasty looking... New battery. Heres the kicker i plug in a code reader and all of my problems go away but code reader doesnt get power. So opened that up and found a orange wire spliced off a harness and into my obd. Found the other end and fixed that. Still only working with code reader hooked up... Any ideas to what someone else has done to my truck? They were stealing power from the trailer braking source but why? To power obd outlet? Any help is appreciated.