Gas Gauges still don't read right

[JZCracker]

Got a 1973 Chevy K20. I've dropped both tanks and replaced the sending units, the selector valve, dash circuit board, fuel gauge and tank selector switch.

I even dropped the tank and removed the sending unit on the passenger side tank and wired it up in my hand so I could test the float and it worked great. When I put it all back together all seemed to work close to accurately. Days pass and my main tank now reads full (likely 1/2- 3/4 of fuel) and the passenger tank is almost 1/2 full and barely reading a quarter.

I'm think it may be a wiring issue when I had to rewired in the fuel selector switch (or maybe a grounding issue)? Any ideas would be appreciated.

 

[Bextreme04]

Got a 1973 Chevy K20. I've dropped both tanks and replaced the sending units, the selector valve, dash circuit board, fuel gauge and tank selector switch.

I even dropped the tank and removed the sending unit on the passenger side tank and wired it up in my hand so I could test the float and it worked great. When I put it all back together all seemed to work close to accurately. Days pass and my main tank now reads full (likely 1/2- 3/4 of fuel) and the passenger tank is almost 1/2 full and barely reading a quarter.

I'm think it may be a wiring issue when I had to rewired in the fuel selector switch (or maybe a grounding issue)? Any ideas would be appreciated.

Fuel gauge could be bad.

The fuel gauge works of resistance in the circuit, any kind of bad connection or bad ground will cause them to not read right. I would definitely check the whole circuit to verify that I had good clean grounds. You should have a ground coming off each sending unit to the frame as well as multiple grounds from the cluster to the parking brake mount. You can also pull the cluster and check the fuel level wire for resistance. Switch between the tanks and see what resistance you are seeing when switching between tanks. If the resistance numbers are out of scale, start troubleshooting back through the circuit until you find the problem spot. If the numbers are correct each tank, you have a bad gauge.

 

[custodian]

Could be a grounding issue. There is a resistor on the back of the gauge that should read between 87-90 ohms. Bad connection somewhere. Looking straight at where the gauge goes, there are 3 connections. The connection on the left is 12V, the connection on the right should be from the gauge (pink wire), the connection on the bottom should be the ground.

I'm not trying to hijack your thread, but my gauge was working, diesel fuel only, until I switched it with one that reads unleaded only. Now only get either empty or over full on either gauge. Mines an 85 C10.

 

[JZCracker]

Thanks Guys... I'm a bit burnt out trying to solve this and just taking a week or 3 break. When I get re-motivated I'll work these suggestions. I'm also guessing it's a wiring issue, but unfortunately wiring/electrical testing is my weak point

Custodian - one thing I have figured out is when the gauge was not getting signal from the sending unit (ie I disconnected the sending unit wire) is always when the gauge shot up past full.

 

[Charlie]

If you are interested in a new fuel gauge, I have an extra one. You can read my post about it and how I ended up with extra gauge. For 73,74, 75.

https://www.gmsquarebody.com/threads/new-fuel-gauge-needle-falls-to-4-oclock-position.24714/