I recently installed a 2003 wiring harness, engine, and accessories, in a 2006 silverado. The stock 06 PCM, TAC Module, and everything else is original. We have everything working except the Cruise Control which is the main problem now. Also the truck takes about 15 seconds to idle normal and will sometimes die or sputter until then when started once warm but I am assuming that is a seperate issue. Also the battery light is displayed which is not a big concern of mine and is probably because the Ground box thing around the negative battery cable (Sorry forgot name) was not used with the new harness since there is no plug for it on the 03 harness. Could anyone point me in the right direction or possibly post a pinout of a 2003 TAC Module and possibly any related voltages/ resistances to check for with the 06 TAC mod? I already have a pinout of the related TAC Plug for an 06 and I would like to compare them. Thanks.

 

Your problem more than likely lies with the harness and PCM swap. You will have to pull pinouts for each harness and compare. If your truck has stock electric fans I dont think they will work correctly either because the 03 computer is lacking the ability to control them.

Or it lies in a tac module difference between the two years. They way to verify would be call a dealer and see if the TAC's are the same part number. From my experience building harness and parts for my vehicles when you start mixing and matching years on computer related you are asking for glitchy little bugs that are a PITA to get ironed out.