Technology being what it was in 69, normal would definitely include the false fickering. Thanks for the option though, spot on!
Had a restored sender that I was planning on using until the repro units became available. Thought folks might be interested in a side by side.
The reproduction unit looks to be a better quality that the original. Stainless helps and there is a small guard over the float lever which looks like it would work better than the two bent tabs on the the original unit and looks more stable.
Hopefully the low fuel thermistor last longer than originals!
I installed mine in a completely empty fuel tank - should the LF light come on with the key on & gauge reading empty? I didn’t want to leave it on for long in case the unit needs some fuel to cool it, but I did wait about 30 seconds.
A couple of notes:
The light does come on during start so I know the bulb is working.
The light worked with my OEM sender until hippie gas ate it (thus the new sender).
Yes, the light should always come on when the unit is not submersed in fuel.
Crap. That’s what I was afraid of. I will check the connector.
No light. I ran wires from the sender to the connector to insure good connections, no light.
The light does come on during start (prove out circuit)
I know that grounding the wire from the gauge will make the gauge read full - Is there any way to test the circuit back to the light or bench test the sender?
Yes there is. Grounding the low fuel wire (thermister) makes the relay click & the light comes on.
So the wiring, components and circuit from the tank is good.
The sender to the tank and the tank to ground continuity is all good, as is the sender to chassis (all checked with digital ohm meter w/tone).
At the sender, I have three posts and it is ‘keyed’ so the connector can only go on one way.
Fuel gauge post = good ground as expected.
Thermister post = open - expected ground.
Third post = ground - expected open.
Ideas?
I just dug out my old XR7 sender (the one eaten by hippie gas) and the posts-wiring match what I am seeing. The third post is ‘riveted’ to the sender plate so getting a ground there makes sense.
Unfortunately the thermistor is destroyed so it’s no good for functional testing.
Figured it out. Working now.
What was the issue?
Be interested as well. Cougar Bill (thanks Bill!) replaced my sender using a combination of original, restored and reproduction senders and the system did not work when i get the cat back.
But next day like a light from heaven the low fuel light came on. Can only guess that since the thermistor works on temperature change it needs to be immersed first before it detects the change?
Believe it or not, my LF light issue was a low battery. Everything worked independently but not together. Stuck a battery charger on & the light came on. Went off after the 1st 5 gallons were poured in.
Unfortunately the the sender shows 1/3 tank when full. No resolution in sight so I am putting my old std sender back in.
So much for unlimited technical support…
Instead of a new thread, reviving this one, around fuel capacity or gas tank size. (Put those there for future searchers).
As i understand it from quoted My 69 has a 20 gallon tank. I have never run it dry, but when the gauge is in red I can only get 11 gallons or so in…meaning fuel comes up the neck. Could it be anything other than a bad sensor?
Thanks
Over time residue and oxidization create an increase in resistance. So when the float arm is all the way up it will show less than a full tank. This is particularly true with the reproduction senders as the design they use is more prone to it.
There were three tanks sizes 16 gallon for '67 and '68, 20 gallon in '69, 22 gallons in '70. Any tank will physically fit in any year from '67 to 70. (The '71 to '73 are a completely different design.)
The senders for each year are different.
The '67 is designed for 16 gallon tanks, uses a smaller 5/16" tube and matching filter. The most common design is prone to wear and it is hard to find a rebuildable example as the sweep arms are frequently worn through. Low fuel senders have the same wiring pin out as the '68.
The '68 is also designed for 16 gallon tanks and was upgraded to the 3/8" tube and matching filter. The internal parts were redesigned and are more durable. These are in demand as they also fit the '67.
The '69 is designed for 20 gallon tanks. It has a longer float arm to be able to reach the top of the tank which is taller than the 16 gallon version. When you put the 20 gallon tank in a 67 or 68 you will lose about 2" of trunk depth where the tank is. The pin out for low fuel senders is different for '69 and '70. You will need a '69/'70 harness to use this sender in a '67 or '68.
The '70 is designed for 22 gallon tanks. The float arm is even longer to work in a tank that is even taller. You lose another inch or so of trunk depth compared to the '69. Pin out is the same as '69.
The '71 through '73 is configured differently and not compatible with the earlier Cougars. All years '71 to '73 are interchangeable.
To answer this question: “Could it be anything other than a bad sensor?”
Yes. The gauge works when a very small heating coil heats up a bi-metalic strip that bends causing the needle to move. Resistance anywhere in the circuit will reduce the amount the needle moves. The gauges are fed by the instrument voltage regulator that puts out pulsed DC averaging 5 volts. Lower voltage will cause the gas gauge, oil pressure and temp gauges all to read low.
You can do a quick test by shorting the harness at the tank to ground. It should peg the gauge above full. Do not leave this very long as it could damage the gauge. If you short out the low fuel wire it will light up the low fuel light. If you put a test light on the gas gauge lead in the harness you should see the light pulsing, this test is really for gauges that are reading empty all the time.
Thank you Bill!