My Fiat 124 to DeTomaso Pantera water temperature gauge transfusion was successful! I was able to retrofit the Fiat guts with simple hand tools and a few hours of work. As DeTomaso parts become more scarce there may be others that will be interested in how I did it.
The first step was to remove the trim bezel from each gauge. So as not to deform the bezel I used a suitable hose clamp wrapped around the outside of the bezel to keep its shape, as I carefully bent the backside open around the entire perimeter with a small screw driver. As a precaution, I had a rag between the hose clamp and bezel and put the worm drive at the bottom of the gauge.
After removing the bezel and two small nuts on the backside I was able to pull the faceplate and internals out.
Next I used a rotary tool to grind the retaining swages off both faceplates.
With the faceplate removed I colored the needle with a green marker and then a green highlighter until a match was made to the original needle color. It appeared that swapping the needle was not possible, or at least beyond my capabilities, so I took this low-effort Route that actually yielded passable results.
In place of the swages I used JB Weld to hold the DeTomaso faceplate onto the Fiat mechanism.
I checked the calibration between the Fiat mechanism, Pantera faceplate and temperature sendor by placing the sendor in a cup of vegetable oil at temperature. I found that the best compromise was having a 57 Ohm resistance between the sendor and gauge. although it reads approximately 20 F low at 190 it enters the red at 240 F and reads fairly accurate at 260 F.
The final product does not look out of place in the dash.
