01-07-19, 07:40 PM
I think you have a short between the three wires going to the tank. Disconnect the connector going to the tank. Does the fuel light go out and the gauge drop to E when the connector is disconnected? If it does it means the short is between the connector and the tank. If the fuel light stays on and the gauge stays past full the short is on the loom side of the connector.
How the fuel gauge works is there's a float in the tank. The float is connected to a variable resistor. When the fuel level is high the float is at it's highest position and the variable resistor is at it's lowest value of resistance so more current flows through gauge so the needle moves towards the full mark on the gauge. If you bypassed the variable resistor completely with a short to ground the gauge would read even higher than full like yours is doing.
The fuel light is a bulb in series with a thermistor. How that works is when the fuel is covering the thermistor the heat that the thermistor generates is transferred into the fuel. That keeps the thermistor cool which causes the thermistor to have high resistance so most of the voltage is dropped across the thermistor and not much across the bulb. As the fuel level drops below the thermistor, the thermistor heats up because now the fuel isn't cooling it. As it heats up it's resistance drops so now less voltage is dropped across the thermistor so more is dropped across the bulb and eventually it gets to a point where the bulb has enough voltage drop across it to light. If you had a short to ground and bypassed the thermistor the bulb would be on all the time no matter what the level of the fuel is, like yours is.
So I think the three wires are joined together causing a short.
How the fuel gauge works is there's a float in the tank. The float is connected to a variable resistor. When the fuel level is high the float is at it's highest position and the variable resistor is at it's lowest value of resistance so more current flows through gauge so the needle moves towards the full mark on the gauge. If you bypassed the variable resistor completely with a short to ground the gauge would read even higher than full like yours is doing.
The fuel light is a bulb in series with a thermistor. How that works is when the fuel is covering the thermistor the heat that the thermistor generates is transferred into the fuel. That keeps the thermistor cool which causes the thermistor to have high resistance so most of the voltage is dropped across the thermistor and not much across the bulb. As the fuel level drops below the thermistor, the thermistor heats up because now the fuel isn't cooling it. As it heats up it's resistance drops so now less voltage is dropped across the thermistor so more is dropped across the bulb and eventually it gets to a point where the bulb has enough voltage drop across it to light. If you had a short to ground and bypassed the thermistor the bulb would be on all the time no matter what the level of the fuel is, like yours is.
So I think the three wires are joined together causing a short.