Fuel Gauge Issues

I'm trying to get the fuel gauge on my '68 to work. The fuel gauge is stuck at the 1/4 empty mark. I've got a working (tested with meter) original 90 ohm sending unit (it's out of the tank for testing) but when connected the fuel gauge doesn't move when I move the float. The ground to chassis is good and the continuity for the red wire that connects to the back of the fuel gauge checks out. However, when I check the other (brown wire) that connects to the back of the fuel gauge and turn the key I don't get any reading. Unfortunatly my wire harness has seen better days and my fuse panel was "rebuilt" by a previous owner so it's difficult to follow the wire back to its source. Does anyone here know where I might look to find where the brown wire traces back to? My electrical skills are limited so any suggestions on how to resolve my fuel gauge issues are appreciated.

the basic test is when you unplug the wire off the sending unit and turn on the key, the gauge should read FULL,,,,,,ground that wire and the gauge should read EMPTY,,,,,the ignition switch feeds the fuse box and from there the wire powers the Fuel gauge, oil, gen and brake warning lights,,,,do they work?  you need power to the gauge, its probably a pink one,,,,,put power to it,,,run the basic test,,,,,,there should be a fuse in the fuse box for it,,,,,,,see what you find,,,,see what you got,,,,,,,see what someone gave you,,,,,,the brown wire should be the one going to the tank,,,,,,

Thanks for the info Doni. I just checked and it turns out my oil, gen and brake and cab lights aren't working. Last I remember they were all working but I guess I haven't done much night driving in my van! I'm going to go do some investigating and will likely return with some more questions...

Hey Doni, when you say "pink" wire, are you referring to a pink wire coming from the battery or a pink wire that connects to the instrument cluster? What's the location (connector) of the wire that powers the instrument cluster?

The ignition switch turns on the fuse box, then the fuse box sends power to the dash,,,,do you have a dash, gauge or fuel fuse? the wire might be pink,,,,,,its the power wire going to the gauge,,,,,and it also would be the wire that goes to the other 3 lights on the dash,,,,,,its not the one on the gauge that goes back to the tank,,,,,,and that feed wire could also be just plugged into the fuse box,,,,,see what you find,,,,,,things could be changed,,,,

I was able to trace the fuel gauge power back to my fuse panel. The fuse isn't blown but the thin green wire that is connected to the other end of the fuse has no power, with or without the ignition switch turned. Oddly, I found a thicker pink wire that was capped that reads 12V??

I also noticed that my cab lights no longer work... Any ideas?

you need power from the fusebox that the key turns on to go to the fuel gauge,,,,,find one and hook it to the fuel gauge,,,pull the cover off the dome light,, see if you got power to one of the clips with the headlights on,,,,,,the headlight switch sends power to the light as well as twisting the knob grounds the other clip on the bulb to turn it on,,,,,,,,so you dont got the stock fuse box in there anymore?

Just wanted to follow up on this post. The previous owner had cut the power to my gauge when he added an aftermarket temp gauge. After some rewiring I was able to get power to my fuel gauge again and discovered my original sender wasn't working correctly anymore. I had Tri-Starr Radiator rebuild my sender and I now have a working fuel gauge... Well almost. With a full tank my gauge reads just above the half full mark. I tested the sender and gauge before installing and was able to get it to move the needle from empty to full. I had read that these gauges were never terribly accurate but this seems pretty far off. I also noticed that the gauge didn't rise until I had put 4 gallons in the tank so I'm guessing my sender just doesn't sit deep enough in the tank. Which is a little odd as the sender and the tank are original and came together. Any ideas how I might get better readings?

Well,,,,,,,if you say the sender worked out of the tank, then the float aint right,,,,,,it acts like its too long,,,,,it hits the top of the tank before the resistor gets to 90 ohms,,,,,,do you have the ground wire connected at the right rear shock absorber? How much did the rebuild cost you,,,,,,

They may have replaced the sender with a new 90 that uses a longer swing of the float arm. Then you'd run into what Don is saying about it hitting high before it should. Vans use one designed for 3/4 swing.

The ground is connected to the frame next to the hole where the fuel hose passes through. The sender rebuild was $180 total with shipping from NY to CA and also included a new seal with the top mounting bracket. Their work looked pretty nice and they seemed to know what they were doing so I'd be surprised if they didn't take into account the length of the float arm. But if I recall the arm traveled all the way up to read full and and all the way down to read empty so maybe they did use a longer resistor winding. Not sure I care enough to drop the tank again... At least not right away. Thanks for the info.

2 things have to happen,,,,,right before the float hits the top of the tank, the arm has to hit the stop tab to send the correct electrical signal to the gauge,,,,, sounds like yours could have the wrong angle on it or just be too long to be accurate to work in that tank,,,,,

Bend the float arm!.... Bend it so that the rheostat is higher in relation to the float (bend the float down)
Doni is right about the relationship between the float, top of the tank, and rheostat stop......
Because it's not coming off empty before four gallons are in, it is probably bottoming on the lower rheostat stop before the float reaches the bottom of the tank.......Needs to be bent down....

The length of the float arm has to be correct to allow the 8 1/2" of travel inside the tank coincide with the F and E tang on the sender,,,that needs to be correct before bending it,,,,,but,,,,,I dont think Clay is too enthused about pulling that tank apart again,,,,,,,,,,

Something dont seem right about this,,,,,,,the company surely must know what they are doing,,,,they should have adjusted the float,,,,you can clearly see where the float needs to stop at Full and down to the end of the pick up tube to Empty,,,,,,,so maybe,,,,,,,,,the sending unit is good ,,,,,,maybe it aint the one that is for that tank or that tank aint the one for it,,,,,,so Clay, do both things look original and stock or does something look newer than being there for 48 years,,,

Can't you open up and adjust the contact point/arm on the resister and dial it in to what you need?

The float has to move  8" from Empty to Full,,,,he says it reads 1/2 when the tank is FULL,,,,that means its 4" off,,,,,He said it looked right and worked right when he tested it outside the tank,,,,,,that would mean they put the correct ohm resistor in it,,,,,for a STOCK gauge,,,,I hope thats what he has in his van,,,,and for $180,,,they should know what they are doing,,,,,so it just seems weird,,,,,,,He started this post with a Gauge/Fuse Box problem,,,,,that might still be the problem,,,,,,not this sending unit,,,,,

Test the sender,,,,,unplug the gauge,,,,take an ohm meter, read the resistance of the tan wire, which is the signal from the tank sender, to ground,,,,if the tank is FULL,,,,it should read 90 ohms if the sender is working,,,,,if it reads 45 ohms, that would mean the sender is lying to you if the tank is full,,,see whatcha got,,,,,,,,

I might add, one has to be careful bending the float arms. They can break.

Thanks all for the feedback. Doni, I'll test the sender and let you know what I get...

There really aint no adjustment on the float,,,,,you have to have the the arm touching the EMPTY tang on the pick up tube,,,, AND,,,,the float touching the fuel strainer to allow the sending unit to squeeze into the hole in the tank,,,,,it pretty much has to be adjusted to even get it into the tank,,,,,and you might be able to reach up there on top of the tank and unplug the sender wire to run some tests,,,,,hook a jumper wire onto the sender terminal and measure Ohms,,,,IF the tank is FULL, it should read 90 ohms,,,,and Clay,,,,,,that is a 22 gallon tank,,,,,,HOW MUCH GAS DID YOU PUT INTO IT?,,,,,,you can cut the wire to run your tests and put it back together after you run the tests if your big hands cant squeeze up to the top of the tank,,,,,,,also, ground that wire,,,,which sends an EMPTY signal back up to the gauge,,,,see what the gauge reads,,,,

I hate having to drop a gas tank too...... Yes, the pump arm won't do it's full travel if it's too long..... My suggestion to bend the arm assumes that it is the correct arm that is currently bent upward from where it belongs. You also stated that the first four gallons didn't lift it off of empty......Since you will likely have the sender out of the tank one more time, you can visually inspect the travel of the float in relation to the known space inside the tank..... The float in Doni's two pics lookas though the float is above the mounting plate when up, and not all the way down to the bottom, when down.
I just got done bending the float arm on my 91 wagon because I want it to read 1/2 when I've got about 5/8 of my fuel left....

Chevy sender's are on the top? That sucks if so, sorry. Reminds me of having to pull the bed off my truck to change a fuel pump, I changed them both while I was at it.

Those 2 pictures are not real,,,,,just some spare parts I put together to tell my story,,,,and its a good idea to bend it up a little so you got a little more gas left than the gauge says,,,,I surely dont want my float to hit the bottom of the tank,,,,,I want it to stop about 1/2" above the bottom and read EMPTY and have a gallon of gas left in it,,,,,,

Doni, you asked about the tank size. I'm pretty sure I have a 16 gallon tank, 10 x 28 x 17 (see picture below)