Do a search under "dpetryk", Dave has a post with a complete step by step including pictures! or you can try insrtument cluster, pulling, hooks, removal and you should be able to find it. He has pics of exactly how the tools work and how they act on the cluster. A couple of screws (up from below) hold the Ambient Temp Module to the bottom of the instrument cluster. Remove the screws and pull the module back and outwards.
You can open up the module and examine the connection between the LCD panel and its driving circuitry, maybe that is the problem? The boneyard is the least expensive source for replacements, the dealer gets around $200 for a new module. You can swap out the circuitry and LCD if you get a used part. Most of the time the LCD is damaged but the electronics are still good so if your LCD display is good you just need a module with a damaged LCD display! Thats the cheapest kind! I have a F display in my 87 SDL and have heard that the only years for F is 86 & 87 SDLs all the rest are C! But I can't confirm that! Good Luck!
P. S. Found this:
How to remove instrument cluster.