Bowtie70SS

Hi all, as my first post I have a problem to present. I have a 2003 Silverado SS and have been recently experiencing what can only be described as a power back feed problem. With the truck turned off I can pull back on the dimmer switch to the "Flash to pass" position and it activates the IGN 1 Relay for some reason. If I turn the key on and pull back on the lever then my fuel pump reprimes, and I can hear the throttle body reposition itself. With the key off pulling back on the lever I see a faint glow on the instrument cluster from the SES light and the e-fanskick onfrom the power backfeed. What this is causing, I believe is a code P1518 which is a TPS sensor mismatch from the DBW system and puts my truck into REP (reduced engine power) mode. My truck can be running and if I pull all the way back on the switch the truck will die...no voltage drop obvious on my scan gauge. I have a 140amp alternator from a H2 on it, 2005 Silverado electric fans powered via 3 relays from the PCM and the AC clutch. I have disconnected that stuff and it did not help. I did hose the engine off recently (maybe the source of the problem) but I blew out the PCM, TB, anf TAC connectors. Could my problem be in the fuse box? I can clear out the codes and wiggle wires under the hood and it "fixes it" for a while but it seems random and I can't tellexactly what idid to fix it. I have swapped the PCM, TB, and Pedal assy (cause of the 1518 code) but I believe that the backfeed is causing a mismatch in the TAC system and putting my truck into REP mode. When this backfeed isn't happening the truck runs fine and with all accessories, AC, stereo, fans, high beams the voltage never drops below 12.9. HELP! I guess my next step will be to take the fuse box apart so I can see if it is corroded or wet inside. Thanks

Dave

PS Sorry for the long post