The Stovebolt Site Forums The Shop Area The Electrical Bay fuel gauge and sender

I've been looking at Stovebolt for a while now, but this is my first attempt at getting specific info for my own project. I have a '49 pickup that we swapped a 250 inline into. We also took the tank out of the cab and installed a fuel tank from a Jeep Cherokee. We are putting in new gauges from Chevs of the '40s and we can't get the gauge to read.

Chevs of the '40s told me the gauge needs a sender that has 0-30 ohms resistance. The original tank sender has just that, but the gauge pegs to empty all the time. The sender from the Jeep tank does this as do senders from '80's trucks and everything else I have tried. The local parts store is no help!

Hopefully someone on the 'Bolt can help me out? Thanks!

CK,

Welcome to the Stovebolt. You have several things going on, so the answer isn't straight forward. The factory configuration for gauge and sender is just as 'Chev's' indicates. Gauge and sender must be matched at 0-30 ohms to read properly. Few other rigs ever had a 30 ohm system that I know of.

The only way your gauge will read properly is with a 0-30 ohm sending unit. Here is a basic test for gauge, wiring and sending unit health.

With the key ON, pull the wire at the sending unit. This should send the gauge to FULL. Leave the key ON and ground that sending unit wire to a clean, good ground. That should drive the gauge needle to EMPTY.

This means the gauge is working and the wire back to the sender is intact. You must make sure your tank is grounded and the gauge has a clean contact with the dash where it's bolted in.

As you can see from the test, if you pull the wire off the sending unit, turn the key ON and see the gauge swing to EMPTY, it's an indication you have a grounded spot in the wire somewhere...maybe mashed under a seat or piece of trim.

None of this jabber addresses the fact that anything other than a 0-30 ohm gauge and a 0-30 ohm sender will work together properly. They probably wouldn't be responsible for the activity you are seeing though, but more along the lines of a inaccurate reading. I hope this helps some...and welcome to the site.

Stuart

Given my lack of knowlege here, that sort of makes sense. Is there a way to test the set-up OUT of the truck? In otherwords, I have the gauge cluster and the sending units sitting on my work bench. I have a battery charger that I am hooking up like this:

I put the "-" clip from the battery charger to the sending unit mounting flange. I connect the "+" clip from the battery charger to the "+" on the gauge. I run a jumper wire from the sending unit to the "sender" on the gauge.

This has resulted in the gauge always going to empty. When I raise the float arm (even with the proper 0-30 ohm sender) the needle raises VERY slightly.

Am I missing a wire connection somewhere? Do the sender and gauge have to be installed in order to work? I wondered about the resistance of a longer wire from the sender to the gauge?

They say ignorance is bliss but this gauge thing is anything but blissful!

CK

CK,

Your bench test is perfect, but I think you also need another jumper, or bonding wire, from the gauge case itself to the sender flange. These two items need to be electrically connected to work.

Most chargers are 12 volts. A stock AD fuel gauge is designed for 6 volts. Chev's does sell one they call out as being built for 12 volts. To complicate matters, some folks have run a stock system on 12 volts with no problems while other have seen the gauge immediately go up in smoke when attached to 12 volts.

I think your gauge will work when you run a bonding wire between the sender and the gauge case. Good luck.

Stuart

Stuart,

THANK YOU! I set up the test on the 'bench with the jumper wire between the gauge housing and the sender body and the gauge worked perfectly.

Now the only thing left to do is to modify the Jeep sending unit to accept the Original Equipment Chevy sending assembly. . .but that's just a little cutting and fitting.

Thanks again,
CK

Rather than start a new thread I'll add my question in here.........

Bought a new 30 ohm. sending unit from one of the OEM Retailers at a swap meet last weekend and installed it today. Different in that it has only one electrical post coming out of it vs. the two posts on my original sending unit. I do not have any electrical experience or any meters to check, so I choose a wire and put it on the post and the other under a screw to act as a ground. Turned on the key and the needle went from below empty to EMPTY.

Did I hook up the wires correctly, or does it make any difference which I attach to the sending unit post?

Many thanks,

Spot

YES it does,
you may have wired the gnd to the sender post. try swapping them. senders work the same way most every electrical system does, hot & common. in the case of a gas gauge the hot comes from the gauge, hot in ~ hot out, but it needs a ground. so the hot travels down the wire from the gauge to the sender post. this voltage transfers across the field resistance of the sender. when the float is high the gauge reads full..... what makes the ground? the sender's arm resistance goes to the gas tank ground. make sure the tank has a good ground. make sure [if you have it wired this way the ground wire from the tank has a good ground.
different manufacturers made their own resistance senders to MATCH the gauge, other wise the gauge won't read correctly.

Thanks Vince. Tomorrow I'll reverse the wires out of curiosity and will look to see where the needle goes on the gauge. Because I only had 1 gal. of gas in the newly refurbed tank I expected it to only register EMPTY if it worked at all. Since it went from below empty to EMPTY I assumed it was working correctly. I'll double check to make sure the ground wire is solidly grounded as well.

Spot

i set mine so it indicates empty but i have a couple gallons left
it's kinda like setting the clock ahead 5 -10min so i'm not late to work.

I am also having the same issue as the first post on the gauge issue. I have the hot from the key switch going in to the post behind the full mark on the back side of the gauge. on the other post the wire goes to the sending unit(measred 12 volts at sending unit) the ground goes from the sending unit tank flange to ground. Seems simple but the gauge will read empty with the key off and even with 3/4 full tank the gauge will only read slightly below 1/4 tank. I noticed someone mentioned an additional wire from the gauge housing to the sending unit(what is ment by that?)

Jack,

I have a little cartoon of the wiring for your fuel gauge...it shows the power from the key switch going to the terminal directly behind the 'E'. This is the reverse of what you say you have done. I'm pretty sure this is the straight skinny!

Stuart

The ground wire from the sender to the guage housing was for bench testing. In the truck the ground would be made through the truck itself. Is the cab grounded to the frame?

If the wiring is correct the problem lies in the guage or the sender. Are they original or new? I got a new guage from Chevs of the '40s and used my old sender. If you are using your original sender, it should read 0-30 ohms. Check it with a meter to see if that is where the problem is.

It is frustrating to run into snags like this, but satisfying to find and fix the problem!]

Craig

If you have a 47-53 fuel gauge, the sender wire is attached to the larger of the two posts on the rear of the gauge.

IIRC, the two posts are the same size.
The sender wire is the larger wire.
One post has/had a red warning label attached to it.