[19Fordy]

Ken, Gently clamp the bulging portion of the sending unit below the bolt flange in a vise with protective jaws making sure that you're not clamping down on the float arm mechanism. Paint an index mark on the lid and the flange and then pry off the top cover using a flat blade screw driver or a brake adjusting tool. You will see the adjustable star wheel and resistor.

DO NOT BREAK THAT CARBON RESISTOR. BUT, do check to make sure it's secured by the little holding prongs. You can check sending unit operation of the sending out of the tank by using alligator clips to wire "wire it up". You can use your trunk latch as ground. You don't have to reinstall the top cap each time you adjust the star wheel. Use an alligator clip to attach the incoming 6V voltage to the long springy brass contact. Be very careful not to break any of the fine delicate wiring inside the sending unit. Place the sending unit on a nice soft towel on your trunk floor when testing. Go slow and make sure you wire it correctly.

I spent about 20 hours last month "playing with several units". Adjust and test by manually moving the swing arm on the unit through its path of travel and compare its movement from FULL to EMPTY locations to see if gauge reads sensibly. Re adjust and test. The readjust and test some more. You must have the patience of a toothache.

Make notes of your adjustments made to each sending unit, otherwise you will get frustrated and start going around in circles confused about what you did. That's why you want to color code each sending unit you work on, even though the sending unit part # is stamped into the flange and is covered by the sending unit gasket. It can get confusing. I use $1 store nail polish. Good luck.