The Stovebolt Site Forums The Parking Lot '60-'66 Trucks Math Problem with Fuel Gauge

Installing a set of Dolphin aftermarket gauges. Came with a new sender for fuel tank, but doesn't have an integrated fuel pickup so I left the existing original one in place. Wired up the gauge, made sure good ground, etc. Full tank shows as 1/3 full. So I'm guessing sender is 0-30ohm and gauge is 0-90ohm. (History major, not engineer) If I am somehow right, how would I reconcile it?

Get a potentiometer (pot)(variable resistor) at Radio Shack rated at 100 Ohms. Install in series (inline)some place on the sending wire. Hook Terminal 1 and 2 together and to one end of sender wire, terminal 3 to other. Adjust pot until gauge reads what's in the tank. Apply a drop of "glue/silicone/etc" to adjustment screw to lock it.

That will only make it accurate for that one spot in the tank.

The pot is adding resistance throughout the range of the rheostat on the sender. The hard part is knowing exactly how much is in tank. Empty it, add a gallon and call that empty. Fill it and call that...well, you know. You can buy a 30 ohm gauge from Autometer and sell the other gauge and sender. But of course, I don't know if this is for a boat, an airplane, a go kart, a TF or an AD or a car. Wrench fetchers should know to state the vehicle. Sometimes that may help those trying help those who ask. In this case maybe doesn't matter, but a good practice to follow. To test this fix don't cut your sender wire, disconnect it from gauge and add pot to it and run a short wire from pot back to gauge. Adjust pot. If it does not work send the bill to Johntsmith.

It will work in that one spot. The problem with the added resistance is that it becomes a set value. The fuel sender acts as a varible resistor changing value as it moves. So you are adding the same set value to each on the diminsing values. That's why matching sending units to the guages are critical.

But in any case getting back to the original problem, his sending unit is offering too much resistance, which when full it only reads 1/3 tank. Adding more resistance is only going to lower the reading, not raise it.

The info I gave is for converting 90 Ohm sender to 30 Ohm Gauge. He says he has opposite. 30 ohm Sender, 90 ohm gauge. The fix for that, since the sender won't work that he got with gauge and he wants to use old sender, is to get a 30 ohm gauge as I said in my other post.

OK, 15 min at radio shack and $3.99. 15-20 min tying in the "pot" and gluing in the sweet spot. I'll run it around and see if the gauge behaves like it should, hangs where it is or does something crazy. Back up plan, go back to dolphin gauges and see if I can do a swap with a different resistance gauge. the website doesn't offer much info. Thanks, guys, for taking the time and brainpower.