wire soldered to top of radiator? S4
 

year 87
model turbo II


what is the wire that is soldered to the radiator at the top of the rad? its on the outlet to the pressure cap that "vents" to the overflow tank

low level coolant sensor wire.

how does it work if its just "grounded" out to it? or is that all its supposed to serve as a ground?

IIRC It's grounded when coolant is full. Open sets off the buzzer.

The wire is not grounded to the radiator itself for the radiator housing should be plastic. The wire is part of the sensor for low coolant so the wire is connected to the sensor and it might appear that it's welded to the radiator when it is actually not.