Fuel Gauge Issue

Should I try squeezing the the plug connections tighter? Or is there an internal failure in the plug.
All my tail lights work good so that ground source is fine. I am grounding my jumper to the outer flange on the sender.
I could try a another ground jumper.

Sounds like the break in the circuit is at the plug. Try squeezing the connectors. the point of the clip leads is to verify that the connection is being made.

Some success. The fuel gauge is now working!!!
I may need to squeeze the Fuel light connection more. I just squeezed the outer opening. Any tips on getting a deeper squeeze?

I use a very small pick, to go in at the edge and then down into the molding. This pick is small, think very large needle size.

Good progress guys, and good tutorial Bill! My fuel tank connector pins were loose too - should have thought of that. On the low fuel light, mine won’t light unless the battery voltage is above 13v. For some reason my low fuel relay needs over 9.5 V across it to close. So I need the car running, or a battery charger connected to see the low fuel warning. Mentioning this just in case you might have a similar relay as mine.

Okay. I will work both connections and see if I can get the Low Fuel Light to work correctly.
I tightened the connection with a pick to a tight squeeze.

I still cannot get the Low Fuel Light to work with the sender grounded and the key in accessory and the float at empty.

The gauge works great.

I will try that as well. Easy enough.

Caliicat - you are brilliant. That lit up my Low Fuel Light after about ten seconds. You and Bill are amazing. I hope others can use this process to figure out the fuel gauge/light squawks in the future. I cannot thank you enough.

Typical pull down voltage is just under 7 volts. Might be that much variation in the relay. Calicat your relay did not have the shunt resistor did it?

This is the kind of discussion that I think makes the forum so valuable. This will stay here pretty much forever and people will find the information they need plus an understanding of the process of diagnosis process.

Nope - there is no shunt resistor or resistor wire on my low fuel relay. Been wanting to get another relay to try. But this one works with engine running, so haven’t spent the money.

Awesome - very pleased to hear it’s working, Halbey!

Question regarding the schematic on post 31. I see a radio noise suppressor choke called out, but that is usually placed at the voltage regulator. On 69 and later models, there’s a 10 ohm resistor between ACC power at the ignition switch and IVR input. I believe that was put in to slow the response of the gauges to voltage spikes and start-up issues. Not sure that this confuses the situation/schematic or not…

Like the voltage regulator, the IVR rapidly switching on and off produces high frequency noise. The voltage regulator has the radio noise suppressor capacitor, and it would make sense for the IVR to have some form of suppression too. So I guess the earlier models used the radio noise suppressor choke as shown?

I had never noticed that 10 ohm series resistance before, but now see it on my 70 schematic. It probably serves two purposes - limiting spikes like you said, and also limiting current as a form of RF suppression. Thanks for noting this!

Very informative discussion gentleman, thank you very much.
I’d like to know where I can find one of these sender units, as my 69 Eliminator has donated parts over the years and I currently have a single pin Sender in my tank, which when full only shows 2/3rds on the guage.
At least after reading this, i have a much better understanding of how each part of the system and the rest of the guages work. I’m probably asking the obvious but I presume the rest of the FoMoCo range is effectively the same in function regardless of appearances?
Cheers for the very informative discussion!

xr7g428 is the guy to talk to about the fuel sender.