I have a convenience control package and would like to get the low fuel sending light to work. I purchased a new fuel sender and the low fuel sensor. Evidently, I am supposed to solder the low fuel sensor to the fuel sender. It is supposed to be temperature sensitive and close the circuit when above the fuel to light the light. Is there a manual or instruction diagram for this? Has anyone had experience on where to solder it to the sender? Any help will be greatly appreciated.
All new senders are non low-fuel senders. As such they do not have the second terminal that goes through the sender flange. The replacement thermistor is intended to replace a bad one on an original low-fuel sender. If you do not have a LF sender to repair or it is too far gone to repair, perhaps you could put a screw with insulating shoulder washers through a new hole you would drill through the sender flange (and attach the thermistor lead to that), but I would not recommend it. Also, this screw would have to be spaced from the existing terminal properly in order to use the original two-pronged plug from the car for use with a LF sender.
What some people do is buy one of my Electronic Low Fuel Indicator (ELFI) kits which work with any working sender (as long as the fuel gauge is working properly). The ELFI develops the LF indication from the gauge reading alone. The kits are $110 shipped. If you would like more information on the kit, go to mercurycougar.net and search on ELFI.
Hope this helps.
Regards,
Bob
Do you have the original sender for this car that has 2 terminals? Ours did and I bought the low fuel thermistor from West Coast and soldered the old one off and the new one to the original sender. I also contemplated drilling a second hole in the new sender and adding a connector but it was way to easy to switch out the low fuel thermistor.
I still have the old unit, but it is trashed. It won’t float and the reostat is stuck on “half full” We determined that a new part was in order. I assembled the parts back in the 80’s from a salvaged Mustang. That fuel sender never worked. We tested the new low fuel sender today and it is closed when submerged, but when released it flips. Is there supposed to be a relay somewhere?
I have also with care transfered the sending unit from the new to the old. you carefully need to dissassemble the new one and then grind on the tube to remove the backing plate from the tube. then disassemble the old one and grind down the mounting plate not damaging the tube and then solder the new backing plate to the tube of the old sender, reassemble and solder and shrink wrap the wire. I have repaired several this way with great results.
@ 1969XR7Vert: Tried to find the ELFI kit on Classic Cougar. It kept sending me to the forum where plenty of people had good things to say about it. I would like to look into the kit, but need a better, more direct address. We fiddled with the fuel sender yesterday and really think that it is past reviving. Cleaning and tweaking didn’t help as it seems to have internal damage. It looks like a new kit is in order.
Mustang,
There indeed a low fuel relay, under the dash, depends on year. (For Cougar at least) On '69 it is on the bottom of the cowl behind the cluster. On '70 it is behind and in the vicinity of the radio.
I will either write something or give you a direct link for more information on the ELFI kit I designed, build and sell. Stay tuned.
Regards,
Bob
Hi Bob, i’m not sure, but on 68 xr7’s, i believe they unplugged the low fuel light on the top console, because the dang thing would light up at every turn from 1/4 tank and less. Someone may correct me though.
Jean
Jean,
That is true not just on 68’s, but most of the years that the function was available. What I did in the ELFI design was to increase the hysteresis of the circuit so that the flashing would be reduced over the original circuit. Actually, thinking about it, I think I can reduce this issue further with a small change/addition to the circuit, I will look into that.
Thanks for bringing this up.
Regards,
Bob
oooff! you got a tad technical on me there… but FINALLY! i got something technically right :yay:.
I just wanted to mention it in case the orginal problem of the thread could also include an unplugged connection. I even managed to learn some more…
good day eh?
Jean, FWIW, “hysteresis” is (in this case) the threshold to illuminate the light is one level and the level to extinguish the light is above that by a certain amount. This way (some, not all) of the effect of gas “slosh” is mitigated.
Thank you sir!
I bought one of Bob’s LF indicator kits. Oh sure… the low fuel light now works, BUT it DID knock out my speedo gear on my T5 tranny. I thought the installation instructions should have warned about that possibility.
WARNING! Use of this kit MAY render the speedometer gear in WC T5 transmissions caca.
Go ahead Bob, claim that there is NO WAY that your kit affected the speedo gear in the T5. 
Just a note that this afternoon I finished developing a mod for the ELFI circuit which ELIMINATES flashing of the LF lamp at threshold COMPLETELY. The mod involves introduction of a ~10 second delay to the fuel gauge signal the ELFI sees. In this way, the sloshing around of fuel affecting the light flashing is eliminated because the slosh does not last that long. This is an electronic version of much the way the fuel gauge works, it lumbers up or down slowly and does not respond to quickly changing readings (which is the reason the LF circuit original and original ELFI flashes at threshold). I have installed the modified prototype in Isabel and will test. Assuming all is well (which I am fairly confident it will be), the enhancement will be included in all ELFI units I sell from now on.
I would also be more than happy to modify anyones existing ELFI for a nominal fee to cover postage and a few small parts, like $10.
Regards,
Bob
Thats cool news Bob. It’s small details like this that take the Cougar and the people that care about them to the next level. Good luck testing it on Isabel.
Steven
How much to come and install two of them?
Umm, that’d run room and board plus a buck-three-eighty.
Sounds good. There may be a little minor restoration work you’d have to do first.
My low fuel light is stuck on as well. It wasn’t when I first got my cougar, but now won’t go off. I did change the float so the gas gauge works now. Perhaps I messed something up. What I might do is just cut the wire and make it go off permanently for now at least. I probably need to get in the tank again, but am not looking forward to it.
Hey, thanks for playing the straight man for me! 
Your situation is PERFECT for one of my ELFI kits. As long as your gas gauge works (and so the fuel gauge part of your sender), you do not need to go back into the tank at all (with my kit). You just replace the cluster IVR with my SSIVR and the LF relay with my ELFI and you will have a LF function that WORKS BETTER than the original circuit ever did or will. Check out my recent posts about the ELFI and find out more.
Regards,
Bob