Electrical: Bench test a gas gauge

[Michidan]

Figured most likely a bad gauge. Because there are so many threads about gas gauge, I've tried to search old posts. I don't find if there is a way to test a SW 6 volt gas gauge, out of the car? I get about 42 Ohms but don't know what to expect.

The sender in 1952 is apparently 0-100 ohms. I'd like to test this also, can you do it at the gauge end of the sender wire when it's not on the gauge? There is some gas in the tank, so if check between that and ground should I see some resistance between 0 and 100? I get nothing.

[Jeff_H]

Yes there are lots of posts on gauge testing (including many by me...).

You can test the gauge out of the car.

There must be 6v applied to the IGN terminal of the gauge with the gauge housing/case as ground. Polarity won't matter. Before doing that, measure the resistance from the IGN to the case and also from the sender terminal to the IGN terminal.

I've posted this info before on '53-'54 gauges and it may or may not also apply to '52 gauges:

IGN to sender terminal R: 75 ohms
IGN to Chassis Gnd R: 98 ohms

Where do you measure the 42 ohms ?

If you have the gauge loose on a bench, and use a 6v battery or other power source (don't use a battery charger by itself) you can hook up the gauge with 6v to the IGN terminal and case ground. Then, connect various sized resistors between the sender terminal and the case. With a '53-'54 guage you will get this:

<E >90 ohm
E 90 ohm
1/4 55 ohm
1/2 29 ohm
3/4 15 ohm
F GND

Yes you can measure the sender at the dash end of the wire. Put your ohm meter on the sender wire and other meter lead on the metal of the dash or the body/firewall. You should then be able to measure the sender and it will vary if the arm is moved. If you take the sender out of the tank, you need to connect a ground wire from the sender mounting ring/frame to the car body to do this.

A bad ground from the sendor mounting flange or poor connections from the gas tank to the car body can cause the gauge to not work. When I rebuilt my '53 I ran a separate ground wire along with the sender wire back to the tank and put a ring terminal under one of the tank to sender mounting screws to ensure I would get a solid ground there.

If the gauge itself is not grounded, you can get the weird symptom where the needle moves slowly up from E to about 1/2 and then suddenly pegs over to past F.

[Michidan]

Thanks for the reply Jeff. I did see some of your earlier posts on the topic I'm not happy to be a new member of the non-functioning gas guage club.
42 Ohms was measured from post to post. The gauge is out of the car and out of the case, the needle sits below empty. I didn't know if this was a relevant measurement for anything, and the shop manaul is no help. I do believe I will try to dig up some resistors and check it.

I measured the sender at the dash end of the wire as you desribe. Ohm meter never moved at all. I should got some reading, depending on the gas level.

This all happened becasue the Runtz was not well grounded and let about 9V go to the gauge. Maybe that messed up the sender too.

[Michidan]

I know own a nice selection of resitors. Gauge is dead.
I'll look into fixing it, but if anyone has a working 1952 Champion gas gauge for sale please send me a PM.

Edit: A couple clicks online and I see our vendors still have these in stock. Which is amazing.

[Schraders]

So Studebaker in '54 was using a 0-90 ohms sender? Did I read that right? My car ('54) was converted to 12 volts years ago. If my sending unit is shot, I should be able to use any 0-90 ohms sender with a voltage reducer at the gauge, correct?

[Michidan]

Help! This is frustrating the hell out of me.
In the picture is the NOS gas gauge SI sent me. The key is on in this pictire, there is a good 6V going to the ignition post. The black clip is a quality , tested chassis ground. You see the gauge rests on the empty stop, and that's all it ever does. I've tried the sender wire, nothing happens. Assuming the sender is also bad, I've tried various resistors from 100 to zero going from the sender post to the case. The needle has never freaking moved.

This is exactly the same behavior as my original gauge. So is the NOS one already dead? I don't know what else to think, but I could use some advice.

[Michidan]

So I trudged back to the shop determined to make something happen.
I got the new gauge to finally register. I had been so, so careful not to mess up this new gauge I never really touched it. But I gave the needle a little flick, and now it works. Guess after sitting for 60 years it may hav been stuck a bit.
Using resistors I can get the gauge to give readings. This is good! The sender however still gives nothing. Buttoning up the dash and moving to the tank. Next project.