Gauge or Sending Unit

[fatmxmnr]

Here's the situation...A couple of weeks ago I put some gas into my 69 LWB and the gas gauge read ~3/4 of a tank. I drove it for a couple of weeks and noticed the gas level going down as usual. Then the next time I checked the gas gauge, it had reset to the ~3/4 tank that I had filled it to previously and is now stuck in that position. Based off of this scenario, does anyone have an idea if it is the sending unit that is bad or the gauge?

[jayman68]

If you take the sending wire off the sender and check the gauge with the key turned on, it should read either completly full or empty. Then if you ground the wire it should read the opposite. I think removed is empty, grounded is full, but it might be reversed. If the gauge responds to both extremes then the gauge is good and the sender is bad.