front differential doesn't engage

Snow is beginning to fall here in Oregon and I've just found that my (new to me) '95 suburban's front differential won't engage. Lights on the console don't light either. I know the transfer case is engaging- it's mechanical and 4 Low is obviously putting the rear end in low range. However it's also obvious that the front end in not kicking in. Crawling under and looking around it appears that there is an electrical feed from the transfer case to a unit that attaches to the front differential. Wires and connectors look fine. #24 fuse (25 amp) side of dash next to the door that says its for 4WD looks OK too. Any suggestions on how I can determine where the problem lies?
Thanks
jbrain

I just fixed the same problem on my 95 Sub. First disconnect the wire harness going to the front diff and check it for 12v when the 4wd selector is shifted into 4wd. If you have a voltage then, you have a bad solenoid. It's a dealer part, so you have to order it. It's not hard to take out the old and put in the new. Good luck. I can't live without my 4WD here in CT and VT.