1. Verify the Sending Unit (Most Likely Culprit):
* Access the Sending Unit: This is usually located inside the fuel tank. It involves dropping the fuel tank (a significant job requiring safety precautions). Caution: Work in a well-ventilated area and disconnect the battery negative terminal before working near fuel.
* Inspect the Unit: Once you have access, carefully examine the sending unit for any obvious damage, corrosion, or loose connections. The float mechanism inside might be broken or stuck.
* Test the Resistance: You'll need a multimeter. With the sending unit connected, gently move the float arm through its range of motion. You should see a changing resistance reading on your multimeter as the float moves. Consult a repair manual (or online forums for your specific truck model) to find the resistance range specifications for your sending unit. Readings outside this range point to a faulty unit. If the resistance doesn't change at all, the sending unit is likely bad.
2. Wiring and Connections:
* Check Wiring Harness: While the tank is dropped, inspect the wiring harness leading to the sending unit for any breaks, chafing, or corrosion. Repair or replace as needed.
* Inspect Connections: Check all the connectors for corrosion or loose connections. Clean with electrical contact cleaner if necessary.
* Check the Gauge Cluster: While less likely, there could be a problem with the gauge itself within the instrument cluster. This is more difficult to check without specialized tools and knowledge.
3. Other Possibilities (Less Likely):
* Ground Connection: A poor ground connection somewhere in the fuel gauge circuit could cause erratic readings or failure. Trace the ground wire from the sending unit to ensure a good connection.
* Instrument Cluster Issue: As mentioned above, a problem within the instrument cluster is a possibility but less likely if the gauge worked intermittently before completely failing.
4. Repair Manual:
A repair manual specific to your 2000 Dodge 3/4 ton with the V10 engine is invaluable. It will provide detailed diagrams, specifications, and troubleshooting steps. You can find these online or at auto parts stores.
Recommendation:
Dropping the fuel tank is a challenging job that requires mechanical skills and proper tools. If you're not comfortable with this type of repair, it's best to take your truck to a qualified mechanic. The cost of a new sending unit and professional labor might be less than the cost of damaging something while attempting the repair yourself.
