As a cougar xr7 owner, I should know this answer. A good place to check is the classic cougar network board. If I find the answer I will post it. I changed the thermistor on my 67 but never had to do anything else.

Me too!

cougrnut wrote:

West coast classic cougar lists a relay for mustangs and cougars. Used, price $45. However, there is a note in the description that says that a low fuel warning light problem is almost always the thermistor. Hope this helps. I will check to see if I have a good used unit, but I don't think that I do anymore.

If you find "the answer" guys, please post it.  A couple of  years ago 68Mustang asked if I could build a circuit to run the fuel warning light.  I tried...I really tried, and thought I had it.  But it failed the bench test and I kind of ran out of gas, as they say.

But you know....with one of those little variable voltage regulator ICs and using  the gas sender as part of a voltage devider and a diode or two and a circuit to set bias on a transistor ..........Hummmmm,   BobE are you out there?  Someone posted the other day that they are the "electrical Chip Foose" or something like that.

Time to chime in.

BB

BB

BobE wrote:

BB - I'm here, but working away from home (where all my stuff is).  Funny as soon as I saw this post I remembered we were trading 'how-to" accomplish over a year ago.  I'm not sure how a thermistor is used for this circuit and would need to see the circuit. 
The gas tank sender is a simple variable resistor so the method you mention should work just fine.  One would need to determine what resistance to set the circuit to trigger.  Could use a bi-stable (flip-flop) circuit also.  However, I'm not sure how the plusating 5volts from the CVU would impact this or any solid-state circuit.  Unfortunately, I didn't get much further, and this job I'm on just keeps going and going, keeping me away from hobby.

Yabutt, the IC regulator is constant...no pulsie.  I just built one and put it in the same box with my relay-controled "use an LED as an alternator lite" device for the new dash harness in the 66.

I'm thinking with a diode to control the current flow, the  sender could  serve the gas gauge and act as the variable part of divider to trigger the transistor  or a bi-sexual....ah I mean bi-stable flip-flop.

All I know for sure is that I couldn't make two crenelamoffins and a couple of veeblefetzers do the job...dang thing kept goin' kravinoid on me.

I do think it would be cool if we could come up with something that could be added on and not have to be in the tank.

BB

Last edited by Bullet Bob (8/15/2013 9:45 PM)

Mark Z wrote:

The thermister is attached to the sender in the tank. When the fuel gets below it causes a current change that then goes to the relay , then the light is lite. I rebuilt the sending unit years ago with new sensor and it worked fine. The gauge is still not accurat though. The part that is giving me an issue now I beleive is the relay.

I'm sure you know more about the Ford system than I do...or  ever will.  Maybe more than BobE know about it also.

Sorry if we got off on a tangent.  We had been sorta working on an add-on system a year or so ago and your post got us all stirred up again.

Hope you find someone with knowledge of that system but I'm afraid I won't be of much help, never having seen it or even seen a print of it.

BB
 

Bob and Bob, this is something I started to work on last winter for my 66. Didn't get to far. R1 & R2 resistors will need to be played with. If you guys don't put something together I'll probablly get back on this when the cold weather rolls around again.

Last edited by wsinsle (8/16/2013 9:02 AM)

BB & MarkZ - thanks for the opportunity to think electronics again.
MarkZ - after my post I starting thinking about the thermistor application and thought that may be how it works.  That being said, the circuit you propose should work.  Maybe when the cold weather rolls around I can back to this also and you, BB and I can share the build.
Regarding the fuel gauge accuracy, I believe the only adjustment is to bend the float arm in the tank (I have the same issue in my 65) ... a trail & error (PIA) process.

351MooseStang wrote:
Personally, I would prefer this type of circuit rather than anything digital. Digital has its place but in this circuit it would unnecessarily complicate a simple and elegant design.

And I agree...mostly.  The nice thing about what BobE and wsinsle and I are trying to do is that it could be added to any car and doesn't require a purpose built sender.

And while we are talking about adjusting the sender to get the gauge more accurate, I developed a set of guides and some distructions a couple of years ago to allow one to adjust the sender to make the gage read where you want it at 3-5 gal. left in the tank.  It requires pulling the sender but it seems to work pretty well...at least it did for me.

I sent it to Dave68 in BC but so far he hasn't  given me any feed back.  It's not perfect (what is?) but if  anyone would like to try it I'll be happy to email it to you.  Just print out the templates, cut out the guides from some stiff cardboard and follow my less-than-totally-clear instructions. 

I made the guides by cutting the top out of the old tank from the 66.   Since all the tanks have the same lower section, it works well for setting up the E mark...which is way more important than any other IMO.

Lemme know via email if anyone wants to test it.

BB

The nice thing about what BobE and wsinsle and I are trying to do is that it could be added to any car and doesn't require a purpose built sender.

That's a good idea, no argument there! Still, if I were to want to incorporate such a circuit into my car I would use the same method that Ford used with the thermistor/relay/light. Of course I'm the crazy guy who pulled his own sending unit and made a new one using a marine fuel sending unit assembly and dash gauge (also using VDO Blue Line marine water temp, oil pressure, voltage gauges and clock). I had to pull it anyway to replace the 5/16" outlet with a 3/8" outlet and I had the new gauges on hand (I used to prototype/design electrical systems in the 80's for a boat/small yacht manufacturer). It would be nothing for me to add a thermistor and a tap out for it at the same time. I try to apply the KISS principle to everything I do but even then I can go gonzo at times, as evidenced by the custom electrical system I designed and put in our Mustang. The only components in my car that have any kind of circuitry in them are the stereo, amps, MSD ignition system and timing control for the headlight shutoff delay. Even then the ignition system is backed up with switches that allow me to bypass the MSD systems and run straight dual point (Ford, of course!).

When the Big One drops on us and we all go Mad Max, no EMP is going to knock my car out of operation. ;)

The comparator circuit designed above looks good though the only thing I would want to make sure of is that there is a dampening circuit (could be a timing circuit) to keep the fuel gauge light from fluttering on and off rapidly when the tank is reaching the threshold for triggering it. One benefit fo the thermistor/relay circuit design would be that it would be somewhat dampened by the nature of the design (heating/cooling cycle is not as responsive as a triggered digital signal). Sometimes the old school stuff is still the simplest and best (for us older coots anyway). I build custom computers for home and business and have been an electronics nut ever since I was a kid so I'm not afraid of new tech at all.

I just like simple stuff in my rig, it's usually more reliable and there are fewer parts to fail.

351 MooseStang  you have a PM

There's a Guy on cougar boards that sells an electronic replacement kit for the relays, which makes the light work properly. I can't find his info, but it is also sold through west coast classic cougars. Might want to give Don rush a call and get some info. I think it should work, unless the new thermistor you put in is bad. I am thinking of getting one of these kits for my cougar. Hope this helps.

So far on cougar board, one message says to check relay and the other says to first measure resistance across thermistor to rule it out. For those who want to make your own relays and controllers,the two circuit boards are clearly displayed on the west coast classic cougar website under electronic low fuel relay indicator.