Kph to Mph control cluster issue

[Trumper]

Hi all, I recently swapped my 1995 kph control cluster to a very nice burr walnut 1999 mph control cluster. Everything sparked up as it should with the exception of an odometer discrepancy, which I knew would happen, but the main issue is the temperature gauge now goes to full within a minute, and the needle wavers & jerks quite a lot on the way to full. The old cluster worked perfectly & the engine is not overheating.
Any ideas as to what could be the cause?
Many thanks in advance.
John

 

[khaos]

What car and are they both from the same model?

 

[Station House]

What car and are they both from the same model?

Good call!

If not wiring could be a gauge/sender incompatability