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gas gauge problems
I install my new tank, new sending unit and put 5 gallons in 20 gallon tank.  My gauge still reads Empty.  I checked sending unit with ohms meter before installing it and it rwad like 9 to 68 empty to full.  The old sending unit reads 6 to 48.
I got the gauge to jump to full one time with old sending unit once.  Does tank need to be grounded?  I put thin rubber pads between top of tank and trunk floor.
I tried putting a jumper across the 2 terminals on the plug at tank but gauge stayed on empty.

How should I go about trouble shooting this?

Sometimes you need to calibrate the sending unit by bending the rod until you get an acceptable reading.
In your case since you have gas in the tank you could jack up the drivers side of the vehicle so the gas doesn't come out of the tank then remove the sender unit and bend the rod downwards a little, reinstall the sender unit, let the jack down until level then check your gauge reading and if close to 1/4 full then done otherwise repeat the procedure.
Also you say new unit 9 - 68 ohms, are you able to get a reading with 1/4 tank maybe 20 - 30 ohms? If still 9 ohms then calibrate your sender, if 20-30 could be earthing or voltage regulator on the instrument cluster.
Perhaps someone will chime in with other ideas but this is what I would do first.
I tried unplugging the plug from the tank (new sending unit is in tank).  I plugged it up to the old sending unit and put the float in full position, gas gauge still stays on E.

How do I test the gas gauge itself to be sure it's good.

If I jump connections on plug to sending unit should the gauge read?

Did it work before you put in the new tank and float ?

73 ragtop, 1999 Mustang Bright Atlantic Blue Paint, Phoenix Engine 302-335HP,  Edelbrock Carb & Performer manifold; c4 with 2000 stall and shiftkit; 3:55 auburn limited slip differential, Hedman shorties; Car Chemistry Exhaust

Classic Air; Tilt Steering Wheel; 1999 Chrysler Sebring bucket Seats ; power windows;
(02-07-2019, 07:20 PM)mudbilly Wrote: Did it work before you put in the new tank and float ?

I don't know if it worked or not.  
I had a problem once with mine where it would read high.  ie It would run out of gas and show 3/4 of a tank.  I found that I had failed to bolt the resistor on the speedo cluster flex cable to the back of the speedo housing.  It had a ground pad that needed to connect.  Once I installed it correctly the problem went away.

[+] 1 user Likes kcmash's post
A couple of things here are unusual. Your first sending unit has an anomalous range of readings, so is your gauge factory stock? If not, all bets are off. The gauge has to match the sending unit. Secondly, the lower value of resistance is when the gauge pegs higher, not lower. 5 gallons of gas in a 20 gallon tank may have a reading of 48 ohms or thereabouts. Thirdly, the tank should be grounded, although the 7123 sending units have a separate line for ground (it is a 2 pin connector).

Thus, one should suspect the ground first. Pull the connector off of the tank and measure resistance from the chassis to each pin: one should be about 1 ohm; the other may be about 14 ohms.

If the ground is good, briefly ground the other pin on the sending unit connector with the key in ACC and see if you gauge pegs high. If it doesn't, it means that there's an issue with wiring or the gauge upstream of the tank.

Once you know the results of this, we can further trouble-shoot your problem and get it fixed.

Let me check your shorts!

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The tank itself will be grounded by the straps, so the rubber pads will not make a difference. The wires from the sender may be the problem but I'm no electrical guy, so just a guess, but is there continuity between them. May have to run a wire from the gauge plug  back to the sender end and check. I could be out to lunch on that but I think you know what I'm trying to get across. I'm damn sure some of the other guys will chime in and clear that up.
If you can get a reading, any reading, I can guide you through adjusting the arm, but for now I have to leave till tomorrow am, Friday.

**What did I tell you. the best guy on here just beat me to the post.**

I learn something new every day!
We may have stumbled upon the problem as I had a Private Message that said the high beam indicator light is always on. I hard-wired his dash cluster, and the OP was responsible for wiring up the pigtail. The line for the power to the CVR is black/green, and the line for the high beam is green/black, and it is fairly easy to reverse these two wires. Without power to the CVR, the gauge won't work, and the high beam will always be on...

QED. I think that is what happened.

Let me check your shorts!

[Image: Flamicon2.jpg]

[Image: oldfart.png]
So, let's assume the gauge now works, but is off a bit. 5 gallons should read 1/4 tank with the car on a level surface. Let's say the gauge reads only 1/8 tank or whatever, the process is you will need to remove the sender without spilling gas all over. For this, you need to jack up the left side of the car as high as possible. I'd recommend using 2 jacks, 1 at the front 1 at the back to lift the car evenly and avoid twisting it or lifting one right side wheel off the ground. then you need to support it with jack stands. I have 6 ton , so nice and high. Once the car is up safely, you can remove the sender, but be careful, gas can still spill out. If the gauge reads lower than 1/4 tank (and if I remember right) bend the arm downward slightly. This will allow the mechanism in the pick-up to read higher. Not sure what that thing is really called, but you get the idea. If you lower the car and it's still off, do it again. It could be a pain in the as*, but if you're like me, you want it correct. After all it's nice to know you can make it to the next gas station!!

I learn something new every day!
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