After the over heating issue we had last month, the water temperature alarm stopped to work. No sound anymore at the start of the engine.
After some troubleshooting it seems it was just a ground issue at the engine block level.
The wire with a resistor broke at one point and it seems to be the culprit for this issue
Ordered some 1K Ohm 1/2W Flameproof resistors:
Rebuilt it and it works great now!