This is another of those items that should come with all boats. It detects whether or not a gas leak exists in the bilge. This is important because starting the engine with gas vapor in the bilge could result in an explostion. This is an easy project, and can be completed in an afternoon.
The first step is to come up with a good location for the gauge. Ideally, it should be at the helm area where it is within view of the operator. The stock factory location is to mount the gauge in the upper console. However, I used that location for my fuel flow meter, so I could not use the wiring harness for this purpose. After locating a spot on the dash, I drilled a 2inch hole and installed the gauge. I wired the gauge to the DC breaker panel so that it is on all the time.
After locating the gauge in the dash, I wired in the sensor. The gauge manufacturer cautions not to lengthen or shorten the sensor, since it is calibrated at the factory to a specific length. While wiring the sensor, I took advantage of wiring brackets located in the starboard side of the boat - above the rear berth.
Lastly, I installed the sensor itself in the engine room. The instructions indicate to locate the sensor as low as possible in the bilge, but above any area where the sensor might get wet - since immersion in water will ruin it. While not in the lowest possible area, I located the sensor adjacent to one possible source of a leak - the fuel flow transducer. I used a left-over piece of starboard from a previous project to make a nifty mounting block for the sensor.
Wiring of the vapor sensor at the helm is as shown below. I won't elaborate a lot on this as installation is fully covered in the instruction manual.
Fireboy M-1 Vapor Detector.