So, thanks for the replies, I've been sick so I haven't had a lot of time to reply.
I just went through the P.87 sequence, tested FBW, AP, Anti Skid, Becs, all switch covers closed, closed the cover over the start button and moved the switch back (starting fuel pump off), disconnected ground power, disengage parking brake....and I still have the DECOL light.
The only discussion I've found in the manual is page 53 where it lists the causes for the light. Possible causes that I don't understand how to fix are:
aircraft is not trimmed for takeoff
emergency trim selected
ANEMO switch is in the off position
I have not changed any trim settings which would eliminate the first two (?). No idea what ANEMO means and a search of the manual returns no results other than the reference on page 53.
This is why I'm confused.
Thanks for any help. And BTW, I love the Mirage.