I have a 1996 zj 5.2 v8 as well, mine is not limited but same diff.
The only thing I can suggest is to take out that 6 cyl one and put either the old one back in and (what didnt work on it just tach side or speedo side?) put up with it.
Or go and buy a new one.
This will be pricey (not sure of the actual price), unless you get an aftermarket one (still will be pricey but more than likely less than a stock one).
Or if you have a pick n pull or something like that where you are then try and find one there... I must warn you... good luck finding that year in an auto wrecker though.
If it still doesn't work even with a new one... then you have much bigger problems to worry about.
It could be your cpu (not good, Very expensive).
Or just a few sending units.
I.E. If its your Tach side (left) then your gas, volts and tach units might all not work, slim but might happen.
If its your right side then your speedo, temp and oil pressure senders might not work.
If the new cluster doesn't work take it in to get looked at.
Any Jeepers in Edmonton, AB
I am on channel 33.