Installed 3G alt and now gas gauge is having issues

When I installed alternator I removed original regulator assembly. I have large power wire and small yellow wire that run to solenoid, then I have the Lt Grn/Red wire from alt connected to original Lt Grn/Red wire. Everything else seems to be working fine and I get no warning lights. Anyone else have this issue or know a fix?

Ignition off:


Ignition on/Engine off:

 

I would think you have an unrelated problem. the fuel gauge and alt. have no reason to be connected to each other.

 

A always full reading generally indicates a short in the yellow/white wire between gauge and tank...

Unplug the connection on tank and if it still reads full, there is a short on the secondary(tank) side of gage... If it reads empty with wire disconnected, problem s inside the tank...

BTW it is possible the gauge regulator on back of dash is causing a overvoltage condition to gauge... That regulator supplies a pulsing voltage to gage that averages 5v, if it isn't pulsing the full battery voltage is supplied to gauge...

 

I disconnected the plug from the tank and gauge stayed at empty. Possible sensor in tank went bad? It's only a few months old. Wondering if I can put a resistor in place to stimulate.

 

A 40 to 50 ohm resistor hooked to tank connector(wire) should give approx 1/4 to 1/2 reading, if that checks out problem is in tank... If it still reads high there is likely a voltage issue feeding gauge...

Have you been inside the cluster lately?

 

I like resistor idea, the harder part is finding one locally. I have not been in cluster for a couple years.

 

Looks like my fuel sender just went, it was only 4 months old. I filled up car and drove around, got a reading of 5.2 ohms and then drove it 20 min to work next day and at end of day still read 5.2 ohms. I ordered a replacement.

 

Yellow wire go's to the battery wire on the alt green/red stripe go's where you have it i just did the swap i put in a 130 amp .no problems all my lites are really bright

 

I ended up replacing fuel sender and problem persisted. The gas needle goes past where you can see when full but when car is lower on gas it appears to read correctly. I also swapped voltage regulator with no change. Any thoughts?

 

Replace the voltage regulator. I purchased an electronic regulator on e-bay for under $20. - look under Maverick, Maverick Grabber, etc.
Of course, you could use a 3-prong 5 volt voltage regulator from a parts house (even Radio Shack), and wire it in.
I work for Garmin in engineering...I got lazy.

 

The regulator on back of gauges? If so I replaced and no change.

 

Disconnect either the instrument panel from the wire plug, or disconnect the instrument voltage regulator.
Disconnect the sending unit wire, from the sending unit (at the tank).
Using an "Ohm Meter", measure the resistance from chassis ground to the sending unit wire. You should get no meter movement. (Use 1000 ohm scale).
If you measure anything, then either the wire has a "short" or there is a conductive contamination from the wire to chassis ground.

Did you replace with an electronic or an original Ford instrument regulator?

 

If it reading correctly at approx half tank, probably the voltage regulator calibration but isn't anything really wrong... You could add a resistor in line from sender to reduce sweep, problem is it's going be a trial and error type of thing... I'll guess something between 5 to 15 ohms would be in the ball park...

BTW if you are resourceful, low value resistors aren't hard to find, a #194 bulb is approx 4.8 to 5.5 ohms... Actual value will vary slightly by mfgr...

 

It's been a little while but I believe if I unplug wire from sending unit gauge drops to empty and if I jumper it or ground it spikes past full. It's a regulator from CJ Pony for 73 mustang.

That makes sense but what I wonder about is why did it read accurately for a couple years and then one day start this.

 

I have a spare gauge. Examining it, it can actually be calibrated (Both empty & full). Perhaps it was calibrated with the "old" regulator (lower than 5V), and when the new regulator/sender was put in, the gauge in now seeing the "correct" voltage.
If you're hesitant to dive into the gauge, "Krazy Comet" idea is great, and easy to follow. In addition, Radio shack also sells a high wattage 10 ohm variable resistor. (Don't know if all stores carry). A 30 ohm 1 watt (or better) + the variable resistor may get you precisely on target. If not, add or take away some of the fixed value resistance.