To help get you started, it sounds like there is a short to ground somewhere along the tan wire from the gauge to the sender. If you disconnect the connector in the rear of the trunk, that will isolate the sender from the rest of the system. If the needle moves to full, then the short is from that connector to the sender. If it stays on empty, then the short is from the same connector up to the gauge.
This week end I tried again to find the problem. I am assuming it is the gauge is bad. I bought a VDO fuel gauge and it is working. Will just mount it under the dash. This will work until I get time to remove dash and replace the original gauge. Only $25 for VDO replacement.