i'm working on the same thing. I called vines auto in alabama. they were very helpful. http://vinesauto.com/
if you can still faintly see a read out all you need is the light circuit board. if the obc is out completely you need to replace it. Vine's has light circuit boards for $25 and obc for $50.00. i need the whole thing : (
gonna try cleaning the connctions first though. they look corroded.
Removal was easy. took about 15 minutes (1990 525).
1) pop of plastic covers on each side of radio, obc, ac area.
2) unscrew 2 screws each side
3) pull right side of plasitc cluster thingy out of dash
4) diagnally (towards passenger side) pull left side out around tabs where the srews were
5) pull radio and radio bracket out
6)pull lever on top of obc.
7)it pops out