MJ 4-banger and Factory Tach

Okay, My brother has a 88' MJ 2.5L 5-speed 2WD. All stock. I scored a factory dash cluster from a 2.5L XJ (don't know the year) from the local junkyard. The speedometer cable will not connect because of a different kind connection. My question is "Shouldn't it be a plug-N-play hook up"? I plugged the connection up and the tach did not work. The MJ had idoit light before, so I know to replace the appropriate sensors, but the tach should work, right?

The speedo connection changed, either mid-year 87 or when the 88s came out. So the "new" cluster you have must be from an early 87 or older. Easiest fix is to replace your speedo cable with the old style cable.

The tach should work.