I recently removed the fuel heater on my truck. There were 2 wires that connect to the heater, and another sensor on the heater housing, and they are wired in series. The wires at this other sensor were melted off, this may explain an occasional blown fuse. What is this sensor for? I assume a thermostat to prevent the heater from overheating but don't know for certain. Also, what is the function of the 2 wire sensor on the lower bowl of the fuel filter housing? The plugs on mine come undone from time to time. And, to all who've never done it: clean the screen under the heater! I was disgusted by the amount of crud in there, it really seems like the screen should have more surface area.

 

One is the water in fuel sensor, not sure about the other by the way you describe it.

 

The other on is the sensor directly above the plug for the fuel heater. And thanks Pat!

 

The sensor wired in series with the heater is the temperature switch that makes the heater come on below a certain temperature. Have seen a couple melted the way you describe. My opinion is that a heater element will occasionally short out and draw too much current, causing the temp switch, and sometimes the heater connector, to melt.

 

thank you.