Mercedes OMC 636 Water temperature sender

[chasmoore]

The water temperature gauge isn't working and I've traced the wire to a sender unit on the top of the engine. The sender has two Lucar type male spade connectors. Which one should the gauge be connected to? What is the other one for? Is there an easy way to connect an over-heating alarm?
Thanks in anticipation

 

[FlorealIII]

The most common arrangement is like this : power is switched to the + side of the gauge , a wire is connected from the other gauge terminal to the sender at the engine , if you have two spade connectors at the sensor the other one goes to the mass .

 

[FlorealIII]

The sensor is most probably a temperature sensitive resistor and so it doesn't matter which connector goes to the gauge and which to the ground , you can choose .