Our Volvos (currently six) have low coolant sensor circuits. Over the years they have saved us from three probable overheating situations.

The 240's are the easiest to install, but the 740/940 series is a bit more of a challenge. Getting the wiring through the firewall on those cars is easiest for me on the driver's side through one of the rubber grommets.

The round reservoir on the 740's is easy to get the switch in place by simply drilling a 3/8" hole and threading the wires through the cap opening. The rectangular reservoirs don't allow that method.

The bracket that holds the reservoirs is different for the rectangular ones. On one application I removed the round reservoir and its bracket (spot welded in place) from a 740 parts car I had. I removed the bracket that held the original rectangular bracket on the 940 I wanted the sensor circuit installed on and attached the 740 bracket with heavy sheet metal screws. Then I installed the 740 reservoir with the switch.

Some rectangular reservoirs on the 940s already have the float portion of the sensor set up in them. You can figure that out by simply removing the reservoir and shaking it. If you hear/feel a rattle it has the float and all you have to do is buy the switch from Volvo and snap it into place.

On my first sensor circuit install on a 240 I included a buzzer with the warning light. Even with an adequate coolant level the sensor switch would close the circuit when the coolant splashed around during sharp turns. The buzzer was very annoying and was quickly disabled.

Randy