>
> now a question if I may... when I ground the sender wire, the coolant gauge
> needle went to the max with a blinking light... - does it mean that the
> coolant gauge is working good? or does a bad gauge could doing that too?
>

A gauge that's out of calibration but otherwise working will respond to
this, but it's running twice the current (about 200 mA) through the gauge
that it's expecting.  If you want a calibrated result unplug the sender and
substitute a 35Ω 5% (or better) resistor.  That should blink the light and
if you wait a minute and tap the cluster a few times should be at the top
marking +/- half a needle width.

Yrs,
d