Fuel gauge help

**65FalconLover** · 10-19-2009, 12:08 PM

The fuel gauge on my '65 Falcon never seemed to read correctly so I replaced it a couple of years ago with a new sending unit and that didn't help. It never read full, but would go up slightly after filling the tank.

I just recently replaced the entire fuel tank with a 16 gal. Jaz fuel cell with a Ford sending unit (70-10 Ohms) and I'm still not getting a good reading. When fully fueled it reads 1/4 on the gauge (stock dash guage).

I've put a Ohm tester on the connections at the sending unit. One is marked "G" the other "S" assuming G means ground and S sending unit. The digital instrument is jumping all over the place.

Does this sound like a bad ground or maybe the wire from the guage to the sending unit is grounding out?

Thanks, John

**bmcd66250** · 10-20-2009, 09:12 AM

Either a bad ground (most likely) or the gauge cluster voltage regulator is going bad. Run your own ground wire to the sending unit and see if that helps. IIRC, grounding the gauge wire at the tank will make the gauge read full if it's working correctly.

**FEandGoingBroke** · 10-20-2009, 02:19 PM

If the Temp gauge works correctly then the volt reg on the dash is fine... They both run off it.

The Fuel gauge power is the same source as the temperature gauge.

**65 BFX** · 10-20-2009, 05:03 PM

Quote:

Originally Posted by FEandGoingBroke

If the Temp gauge works correctly then the volt reg on the dash is fine... They both run off it.

Did you replace the gauge itself yet? Couldnt tell from your post. Thats the last thing possible really. The ground for the gauge is the same for your other instruments, so if anything else works, its not the ground in your dash. Make sure the ground for the sending unit is to BARE metal, not painted. Good luck.

**65FalconLover** · 10-25-2009, 04:09 PM

I'll check the ground again, it might not be the best. As I mentioned I'm getting readings, just nothing that makes sense. On a full fill it reads under 1/2 tank. I've already run out of gas once so I'm hoping to resolve this ASAP. With a foam filled fuel cell it's kind of hard to tell where you're at once the level drops under the foam and sticking my hand in there is getting old. ;-)

John

**Rich27028** · 10-25-2009, 04:21 PM

was your new sending unit a 5 om unit-- -it has to match the guage--

**bmcd66250** · 10-25-2009, 04:46 PM

I had a gounding problem with mine. I soldered a 90* 1/4" Faston (Quick connect) tab on the outside of the sending unit then ran a ground wire that I can plug onto the Faston tab.

**oneputtster** · 10-25-2009, 07:23 PM

I'm with bmcd. I have a 65 and IIRC the dashboard regulator was only regulating the fuel gauge.

One thing it does is reduce volts to something like 5v to the gauge. If you can rig up 5v from flashlight batteries ande use that source instead of the car battery, that might let you test the gauge and sender.

**blkfrd** · 10-25-2009, 07:54 PM

Quote:

Originally Posted by 65FalconLover

I've put a Ohm tester on the connections at the sending unit. One is marked "G" the other "S" assuming G means ground and S sending unit. The digital instrument is jumping all over the place.

Does this sound like a bad ground or maybe the wire from the guage to the sending unit is grounding out?

Thanks, John

Do you mean you put the tester on the connections at the gauge?

The voltage regulator works by closing (12v) then opening (0 volts) then closing (12v) and opening (0v). With an ohm meter on the connections the meter will be jumping all over the place. The VR is just a bi-metal switch very much like a turn signal blinker.

**oneputtster** · 10-26-2009, 05:17 AM

That was pretty interesting, blackford.

When you switch to an autometer fuel gauge it works ok without the VR, so there one built in?