Topic: 1967 convenience low fuel light remains on

[3stangs2fordtrucks]

Hi, this is my first post to your forum. The forum is quite impressive.  I spent last night reading on your forum the information related to the 1967-68 convenience package.  I am presently trying to trouble shoot my convenience system on a 1967 GT390 fastback.  The car is disassembled so I can dig through the wiring fairly easily.  Three of the lights function properly but the low fuel light comes on when I attach the battery to the car and remains on.  I understand from previously posts that the main cause of failure is that the low fuel sensor fails; however, I have a new low fuel sending unit that I purchased from WCCC.  I have also replaced the low fuel relay with a nos one.  To test the low fuel system, I have suspended the sending unit in a bucket of water so that the sensor is submerged but not the top of the unit.  I grounded the sending unit to a frame bolt.  Nothing I have done will result in the light going off.  If anyone has advice I would appreciate it.  I must be missing something.

[jwc66k]

First, welcome. That's a real "downer" entrance.
I went thru this low fuel light circuit on a friend's 67 Fastback a few years back. It was the Thermistor.
For your situation, my first recommendation is to disconnect the low fuel relay with power applied. The low fuel light should go out.
Another sanity check (relay back in) would be to look at the solenoid. On the stud that goes to the starter there is a ring lug connection wire that provides a circuit check function for the low fuel light. That lug can be attached to the battery side of the solenoid by mistake which will keep the light on. A visual check.
Good luck.
Jim

[67gtasanjose]

First, welcome. That's a real "downer" entrance.
I went thru this low fuel light circuit on a friend's 67 Fastback a few years back. It was the Thermistor.
For your situation, my first recommendation is to disconnect the low fuel relay with power applied. The low fuel light should go out.
Another sanity check (relay back in) would be to look at the solenoid. On the stud that goes to the starter there is a ring lug connection wire that provides a circuit check function for the low fuel light. That lug can be attached to the battery side of the solenoid by mistake which will keep the light on. A visual check.
Good luck.
Jim

Good guess Jim, you beat me to that answer! I hope this is it.

If you GOOGLE "Mustang low fuel schematic", you will find some help. It helps to also understand where the wires are SUPPOSED to go.

[midlife]

First, welcome. That's a real "downer" entrance.
I went thru this low fuel light circuit on a friend's 67 Fastback a few years back. It was the Thermistor.
For your situation, my first recommendation is to disconnect the low fuel relay with power applied. The low fuel light should go out.
Another sanity check (relay back in) would be to look at the solenoid. On the stud that goes to the starter there is a ring lug connection wire that provides a circuit check function for the low fuel light. That lug can be attached to the battery side of the solenoid by mistake which will keep the light on. A visual check.
Good luck.
Jim

And beat me to it as well.  +2.

[ruppstang]

That was my first thought too but he stated that the other three lights were working.

[midlife]

That was my first thought too but he stated that the other three lights were working.

It is only that line to the starter solenoid that powers up the low fuel light as a proof-out circuit while cranking the engine.  The other 3 systems have nothing to do with that circuit.

[ruppstang]

It is only that line to the starter solenoid that powers up the low fuel light as a proof-out circuit while cranking the engine.  The other 3 systems have nothing to do with that circuit.

Thanks. I was not aware of that LOL and I have it in my car.

[3stangs2fordtrucks]

Thanks, I will check it out first thing tomorrow. 

[196667Bob]

Thanks. I was not aware of that LOL and I have it in my car.

Marty : Maybe the attached might help clarify it. Note that the red wire from the starter solenoid only goes to the plug for the low fuel relay (and thus the low fuel bulb) ; the blue w/red stripe wire (shown in violet) from the ignition switch  provides the "hot" side to the other 3 bulbs.

Bob

[ruppstang]

Thanks Bob,
I probably knew that 12 years ago when I restored my car, just remembered that the red wire was the test power. I do not drive that car very much.
Marty

[jwc66k]

The wiring diagram posted by Bob is slightly different than the one in my 67 Mustang Electrical Assembly Manual (AM0018 pg 107, E7-8855-1) dated 1-5-67, which indicates a different view of the low fuel relay, namely only one resistor, Bob's picture shows two. I think it's the same resistor, and is most likely incorporated into the harness.
Jim
Looking at the assembly drawing (Am0018 pg 55, E7-8618-1, view B), you can see what might be a resistance wire at the relay connector.

[196667Bob]

Jim : The two resistor symbols on my drawing are on the same wire - it forms a loop. Since it was so close to the main harness, I guess the second resistor symbol was added t0 show that it was a continuation, not a separate wire from the main harness. Your drawing clearly shows the separation, so no need for the second symbol on the same resistor wire.

Bob

[196667Bob]

Thanks, I will check it out first thing tomorrow.

Should you find that you have the system wired correctly, the only other things that I can think of are 1) that the Relay contacts are stuck shut, or 2) the Relay itself. I know you said earlier that you had an NOS Relay ; is it stamped C6AF-10A968-A ? The reason I ask is because there were 4 different Relays used for different 1967 and 68 applications (see attached), and none were interchangeable. Each had their own use, and none was ever "Replaced By" another. Each part number was unique and used until it was deemed "NR"(Obsolete).

Bob

[3stangs2fordtrucks]

Hi, you guys were correct.  I had incorrectly attached the wire to the starting solenoid.  I attached it to the correct side and the light went out.  I am not sure it works correctly now because when I took the sending unit out of the bucket of water the light did not come on.  However, I may have a grounding issue since the system is just laying in the car and the indicator lights, relay and sending unit are not attached.

 I am on the way out of town for the weekend to play with grand kids (higher calling) but will check it out Monday.

The nos relay is indeed C6AF-10A968-A.

I really appreciate the interest and excellent advice you guys have provided.  I would never have figured this out.  I am strictly a newbie.  Thanks again.

[3stangs2fordtrucks]

Hi,  Well, I am still chasing dead ends.  I can't get the low fuel light to go on regardless of what I do.  I removed the starter cable from the starter solenoid so I could turn the key on easier.  Using the 1967 Osborn Electrical Assembly Manual as a guide, I found that wire 365A has power at the Low Fuel Relay and that wire 366 from the starter solenoid does not apparently even when I turn the key to start. I rechecked the ground  (wire 57) to make sure it was good (re-sanded the attachment spot).  It appears to be good.
I am not sure how to test the system since I am not sure what happens when the sensor is out of the gas (water??).  Should the light be on if it is dry and then go out when submerged.  Not sure what the plan of attach should be.  Thanks for your help.