You don't really need the wiring harness if you are comfortable with wiring.
What you will need is a full sweep temp sending unit. Full sweep meaning the gauge needle will sweep across the whole face of the gauge. I think you would be safe with a 250 degree to 360 degree sweep. Just be careful as there are a ton of the 90 degree sweep temp sending unit
I think the oem is 5269870AB. Otherwise try Wells SU3207 or the dealer for the oem part.