Fuel Gauge Issue

[1stford]

Hoping someone might be able to lead me in the right Direction. I have a 1936 Ford truck. Everything is new, but I have a fuel gauge issue. Its never worked but I"m just now getting around to messing with it.

When I turn the ignition on the needle slowly goes up, it passes the F and goes out of view. It stays there until I turn the power off and it goes slowly back down.

I checked the sending unit with an OHM gauge and it appeared to be 23 OHM's at full. It has a good ground to the frame. It's a 6 Volt system. When I got the parts the Fuel gauge was already restored so I have not checked anything on that front.

Thanks,

[Brian]

The [King Sealy] fuel gauges as fitted to 1936 Fords, do not operate via resistance. You have a short somewhere. Feeding a full six volts into the gauge will make it read full. try running a temporary wire from gauge to tank unit. If the gauge then reads correctly, the issue is in the original wire. If it still reads full, the sender unit is at fault. Happy diagnosing!
edit; I assume you're using original gauge and sender unit, the modern replacement tank units are not really compatible

[1stford]

Originally Posted by Brian

The [King Sealy] fuel gauges as fitted to 1936 Fords, do not operate via resistance. You have a short somewhere. Feeding a full six volts into the gauge will make it read full. try running a temporary wire from gauge to tank unit. If the gauge then reads correctly, the issue is in the original wire. If it still reads full, the sender unit is at fault. Happy diagnosing!
edit; I assume you're using original gauge and sender unit, the modern replacement tank units are not really compatible

Thanks for the response. The wire is apart of a new wiring harness I bought for it. It has original tank, original gauge and sending unit from somewhere like Bob Drake Im sure.

[joe 1950]

don’t know if this will help but i’ve always checked the unit like this take the wire off the sender with key on ground the wire gauge should go to empty open wire goes full this will confirm that gauge and wiring are ok sender is the problem good luck

[JayChicago]

Originally Posted by joe 1950

don’t know if this will help but i’ve always checked the unit like this take the wire off the sender with key on ground the wire gauge should go to empty open wire goes full this will confirm that gauge and wiring are ok sender is the problem good luck

I believe the above is incorrect. Grounding the sender's wire should make the gauge go full. Open sender wire, gauge should read empty.

[rotorwrench]

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The modern replacements are all variable resistor units but they don't have a wide enough resistance range to control the King Seeley indicator units with precision required. It's always either too little resistance or too much.

The King Seeley sending units all use a bi-metallic strip with a small heating coil (some exception for coolant temperature units) that rapidly opens and closes a switch. The switch is just a very small set of contact points. In the case of the fuel quantity application, the float arm manipulates the tension on that bi-metallic strip. The frequency of opening and closing is variable according to the pressure applied to that bi-metallic strip so it controls current from very little current flow to somewhere near full current flow. If you look inside one, you will see calibration resistors in there that further control the current level. King Seeley instrument systems were very reliable and kept the electrical parts out of the fuel, water, and oil.

[joe 1950]

jay chicago i stand corrected your right you know you use a technique for so long and then when you get in your 70s things don’t always come out of your memory as they went in but thanks for the refresher course

[corvette8n]

Your never going to get an aftermarket sending unit to give you accurate information. The best you can do is bend the arm so it shows when it’s mostly empty. I ran out of gas with mine and tried a couple aftermarket senders. Unfortunately when I bought the car it had an aftermarket sender in it.

[t35]

i have an after market sender, it works good at idle but when i rev engine gauge goes up past full. would a resistor do the trick? 1936 ford