did you get the correct sending unit? there is one for the light on the dash for about $5 and one for the gauge for about $15. its just a thought as the previous owner had put the wrong one in on mine and thats what i had.
If you have the correct one and dont have a connection (wire) problem then as stated it likley to be the gauge in the dash i would think.
4" clayton long Arm, 5 inch rear stretch. CRAWLER tank. 35" KM2 muds, 1" MML from Brown Dog. Rear D44 Locked with a Detroit & trussed on Alloy Shafts, 4 point triangulation. Rear disc conversion. AtoZ Cage. Rubicon OR241 4:1. Front D30, Polly Performance Sleeve kit, locked with ARB, Alloy Shafts and HD steering linkages. Clayton belly up and oil pan skids, PSC Rocker Knockers, ORO air powerd Swayloc, Onbard Vita 450 and tank for fills and ARB compressor for the locker. Covered in dents.