Initially (with old battery still in), the Cluster and Interior would light, but when Ignition turned to START, all power would drop...leaving only the flashing red Security light.
After battery was replaced, Cluster and Interior would not light, and red security light comes on fast flash immediately. Topped off battery to ensure proper voltage and max cranking amps, no change.
I connect terminals to each other for several minutes
Then connect to battery...get fast flashing security light
Turn Key to START, security light turns solid and becomes dimly lit

A few strange things we've tried from forums:
Use Sentry Key to Lock/Unlock Driver door Lock, also the Double Unlock technique and crawling through Passenger door to Lock/Unlock Driver door manually.
Removing IOD (Fuse 51) for several minutes.
Remove/Replace SKIM Fuse
Checked Wires to PCM
Connecting Terminals to each other for hours