speedomter/odometer not working

Guys,
I'm kind of a dummy when it comes to cars, but know a tad bit about them. Anyway, I had to change the battery out on my 98 ZX2. The original battery finally died, believe it or not. Anyway, there was quite a bit of corrosion that I remove a lot of thanks to baking soda/water combo. Anyway, everything works now except the speedometer and odometer don't work anymore. I noticed that there is a little black box that is connected to the negative battery cable, but don't know what it is. Could something in this box have gotten fried and that is why the speedometer/odometer doesn't work? From what I have read, a bad Vehicle Speed Sensor can cause this. I just had some sort of speed sensor replaced on the tranny that was making my car not shift right. Anyway, any advise would be greatly appreciated. Thanks.

I just had to get my speedo fixed- it was hella expensive though. I had shorted out a "circuit board." It was a professional job though, I wouldn't have the slightest clue how to do it myself- electric shorts can be a bitch to find... good luck, lemme know how it goes!