I have a 1988 Buick LaSabre. two days ago my wife had pretty much the same problem. service engine soon light came on, no power, no speedo. I took it out later that night and it worked fine. I took it to work today and had the same problem she did. ( thats why Im looking in the forums now). If you find out anything PLEASE let me know.
TKS!
Update, I saw this. Hope it helps.
http://www.automotiveforums.com/vbul...ht=speedometer