There has been a lot written about installing cruise control for a DBW Gen3 LS engine. You can find one piece in one thread and something else in another. I will try to put it all together in one article. This has been my experience install a 2002 LS in my 55 Chevy. I have attached a picture to this article. First thing you need is a cruise switch. There are 2 types of cruise switches, closed circuit and open circuit. The Gen3 wiring harness is looking for a open circuit switch but most of the aftermarket switches are closed circuit. This is a link to a site that show you how to determine what type of switch you have. http://www.rostra.com/manuals/250-1223Form4565G.pdf
If you have a closed circuit you will need to add 2 relays to correct the signal to the TAC module
The next problem has to do with LED brake lights. The brake signal wire that comes from the ECU has to see 12V when the brake is applied and Ground when brakes are not applied. This is a yellow wire if you have a PSI wiring harness and light blue if you have Painless, Speartech or other harness.
The next wire that must be connected if you are using a automatic transmission is the Torque Converter lock up. This wire must have 12V when brakes are not applied and open when brakes are applied. You can add a dual brake switch or add a relay. This is a purple wire from the ECU on all the wiring harness that I have used.
I also wanted to activate the cruise indicator on my Dakota Digital gauges. This requires a ground signal to activate. I have not found anybody that know how to get this signal from the ECU.
After many hours and 6 relays I was able to get the cruise to work but where to you put all this stuff. This small 2"x3" box solved all my problems. It works with closed or open switches, corrects the LED brake light signal, adds Torque Converter and Cruise Indicator signal. Hope this helps.