Fuel Sending Unit

My gas gauge on the dash has gone haywire. It reads full tank all the time. I know there is a way to determine if it's the gauge or the sending unit. I do suspect a bad ground. Car has 131k I hate to pull the tank if not needed to, but is this a problem with Trans Sports I have a 95 SE witht the 3800 Motor Thanks in advance:popcorn:

May be this can help you do some tests. (diagrams for '93 but I'd be very surprised it would not be the same)
www.avigex.ca/xport/instrumentpanel.jpg
www.avigex.ca/xport/C200pinout.jpg
www.avigex.ca/xport/C200location.jpg