how to replace bcm on 99 grand am

Hello, I have a 1999 grand am se, with the 3.4L v6 engine. A few months ago, I starting have gauge/light problems, (random gauge resets, cruise would disengage, HVAC turned off, etc.), and it started to get worse and worse. Checked connections to BCM, all good. Problem kept getting worse. Went to rockauto.com to buy new bcm. Disconnected battery, replaced bcm, lights and gauges come on, but engine won't start - just cranks.
Is there anything I'm supposed to do to get the new bcm to work with this car? There were no existing engine problems before this change, and I have not put the old bcm back in. Can I put the old bcm back without screwing the pcm up? My autoxray scanner doesn't pick up any trouble codes up at this time.

Thanks for any help!

- Eric

I don't have the answer to your question, but I'm having a similar problem to the one you tried to fix on my '99 Grand Am that has even the dealer baffled. I lose my gauges and HVAC at random times while driving. At high speeds, I'll also feel a slight hitch to the transmission when it happens. Lately it got worse to the point where now, the gauges are gone more often than they're working. What is the BCM and where is it located?