Hi Blue. At apx 1/2 full you should get around 15 ohms of resistance, so it sounds to me you may be pretty close with 10 (since we don't know how close to 1/2 full you are). Furthermore, it is really good news if your sending unit is registering between 0 and 30 ohms and not rubbing on the side of the tank or hanging up anywhere. If the float rod is adjusted so that it comes very close to hitting the top of the fuel tank when the tank is full, all will be pretty much Jake. One thing that occasionally is overlooked: These fuel tanks have no baffling to keep fuel from sloshing from side to side, so that means when you open the door, stand on the running board and sit down in the driver's seat, the truck leans a bit to that side (which it will do even if you're built like Frank Sinatra). So when that happens, the sloshing fuel will create sort of a mini tidal wave effect in the tank...and it will slosh side to side for a while, too. Which naturally will move the float up/down as the fuel moves side to side. Could just be that causing the needle to move from just below E to just above E.
But here's another thing. Inside your fuel gauge is an hourglass shaped permanent magnet which is moved up/down by electromagnetic force. That little permanent magnet will have its magnetism changed if your fuel gauge was run on 12v in its life at some point. Then if that happens (and some think it could take a few minutes to a few hours) your fuel gauge will work fine with 12 volts but might register lower than it should on a reduced voltage. True your fuel gauge cares more about amperage than voltage, but still in all the two are interconnected. For many years I've told folks to think of voltage as the size of your arm and amperage as the strength of your arm. Anyway, if your gauge seems to be registering lower than it ought to, you might try removing the Runtz device and see what happens.
