as he said, should plug right in...HOWEVER...
if your tach is not working, check the fuse for the back-up lights. That fuse pops, say good-bye to your cluster until it's fixed. Cluster is put on there to avoid shorts. But since I'm sure your reverse switch was wired, you probably shorted to ground and fried the fuse. It should be red, 7.5AMP fuse under the dash. Replace it. If it still doesn't work, you have a problem somewhere else. Also check to make sure reverse switch is not grounded to the block/trans.
-Brian