golf 1 cabrio (155) 2H motor temperature light flashing
 

my GolfMK1 with 2H motor has the temperature light flashing. Temperature gauge is in the middle, fan works, temp is ok.
Coolant reservoir has no possibility to mount a coolant level sensor. But there is a connector present. So the reservoir could be replaced. Can I connect the 2pins of the connector with a wire (or will it create shortcircuit)?
Or better to foresee a resistor? But which is the resistance ohm value?