Coolant expansion tank wires

Can anyone tell me what the wires are for that are connected to what looks like a sensor on the top of the coolant expansion tank on my Mk1 GTI?

According to my Haynes Manual the coolant temp sender is screwed into the elbow of the water pump.

Is one for the needle guage on the dash and one for the MFA?  If so, which is which?

Thanks

the one obn the expansion tank is a level sensor

Thanks for the quick response!

What happens if it detects that the coolant level is low?

light in temp gauge comes on