Coolant gauge stuck

Just recently, my coolant gauge on my 2003 ZX2 stopped responding, it's stuck in the middle between Hot and Cold, even after sitting overnight in mid-50 degree weather. Coolant quantity is right where it's supposed to be...

I bought a replacement temp. sending unit and slaved it in and no change--the gauge doesn't budge from where it's at. I'm planning to return the sending unit...

Can this gauge be changed out solo, does the whole instrumentation cluster need to be changed, or is there a stupid-easy fix ( a wire / relay / module / widget / connector) that I can replace/repair myself? Not really sure which way to jump with this problem, thanks in advance!!

javaman63