You guys need to start new questions, and please be sure to list the engine size and mileage. This was a private conversation between two people, eight years ago. We see it as having received a reply, so none of the other experts are going to read your additions or have a chance to reply. You won't get the help you're looking for.
There's two places to look for a replacement instrument cluster. The first is any salvage yard. I'm fond of "Pull-A-Part", but they don't have any yards near me. Do a search for them and see if there is a yard near you. You pay your buck, take your tools, and you can spend all day there if you want to. I've been to 16 of their yards. All are very clean and well-organized.
Be aware instrument clusters are no longer the simple, reliable units they used to be. They are entire computer modules, and cars are the worst possible environment to be planting unneeded electronics. Failures are very common, and there's a good chance a used cluster from a salvage yard will develop the same problems. A better alternative is to buy a remanufactured cluster with a warranty. If you do a search for "GM instrument cluster repair", you'll find dozens of shops that specialize in them.
For the discussion on relearning the anti-theft system, the steps were correct, but they didn't go far enough. Best is to connect a battery charger set to the lowest range because this takes 30 minutes.
Crank the engine briefly, then release the ignition switch to the "run" position without turning it off. The "Security" light will flash for ten minutes. When it stops flashing, turn the ignition switch off, then immediately crank the engine again. Release the switch to the "run" position again, then wait another ten minutes for the "Security" light to stop flashing. Do that a third time. The next time the ignition switch is turned off, then back on, the anti-theft system should be off, and the engine will start and stay running.
That is from memory. If it doesn't work, try doing the steps with never turning the ignition switch all the way to "off". This procedure is used to relearn the Passlock sensor after it has been replaced, and possibly for some other, related things. If the system arms again, it is either because there is a problem that needs to be diagnosed, or my instructions are not accurate.
Saturday, April 1st, 2017 AT 10:19 PM