Fuel gauge for main/Aux tanks help

[alvald83]

I am trying to get my fuel gauge to read both of my fuel tank sending units. Since ive had my truck I've only been able to read the main fuel tank behind the seat. I replaced the fuel tank selector switch (under the dash) a few months ago, which didnt solve the issue. I decided to live without the ability to read the fuel level in the aux. tank.
Today i removed my gauge cluster to install LED bulbs and found an orange wire not connected to anything. From the wire diagrams that i have seen it seems that it should be going to the cluster, but there is another orange wire in the cluster harness going to the fuel gauge.
The 1st image shows the orange wire that is coming from the selector switch. The 2nd image shows the orange wire from the harness that goes into the fuel gauge on the cluster.
The confusion that im having is that the wire diagram shows the orange wire from the tank selector switch going to the fuel gauge on the gauge cluster.
Any ideas?

20201123_153359.jpg

Gauge cluster.jpg

[390FE1972]

Here is the gas tank wiring diagrams for the 1969 trucks: http://www.fordification.com/tech/wirin ... x-fuel.jpg

Hope this helps!

[cash667]

Please double check if the orange wire in your first pic has a white stripe?

If it is clearly an orange wire from the aux switch circuit I think it has to be connected with the aux sending unit wire. Follow it up starting at the aux Tank and see where it ends...


Cheers
Chris

[alvald83]

When i look at the wiring diagram that was presented by 390fe1972 in his reply, it shows the green and the green-red stripe wires coming from the switch each connected to both fuel sending units. My confusion is which orange wire do i connect to the switch, the orange wire from the switch or the orange wire included in the wire cluster harness on the cluster. My thoughts are maybe the orange wire on the cluster harness is used when the truck only had 1 fuel tank.
I just wanted to exhaust all possibilities before having to drop the aux tank and replace the sending unit.

[cash667]

first question: is anything happening when you toggle the aux tank switch? Needle moving to empty in one switch position?

if yes:
I think what you see in your first pic is connection "C" in the wiring diagram. So this orange wire could be the "input" to the switch from the aux sending unit.
What you see on your second pic is the cluster connection. This orange wire comes from the main cluster connector "A" where it is supposed to be when there is no AUX tank present.
The question is, if somebody has connected the orange wire from the main cluster connector to the aux tank switch. The easiest way to find that out ist to unplug the connector directly on the aux switch and test all pins on continuity to the plug on the back of the cluster.

if not:
Maybe your on the right track that your truck has not a factory aux tank and somebody did an upgrade later on.
Than you need to find the two orange wires coming from each tank. One should come from the A pillar and the other from the main harness going through the firewall. Both need to be connected to connection "C", one is a single male plug and the other a single female.
On the big connector directly on the switch there should be another single orange wire coming out of the connector which needs to be plugged on the cluster.


hope this was not to confusing..

Cheers
Chris

[390FE1972]

Do you have the long orange wire coming from your aux gas tank sending unit going up into the engine bay? It is about 8 foot long and plugs into the aux gas tank sending unit. It is also grounded to the frame near the aux gas tank sending unit.

Here is a picture of the plug that goes into the gas tank selector switch (toggle switch) on a 1967: http://www.fordification.com/forum/view ... =8&t=78682


Regards

[390FE1972]

Here is a picture of one of the 8 foot aux gas tank wires on e-bay: https://i.ebayimg.com/images/g/gZAAAOSw ... -l1600.jpg

Regards

[alvald83]

Hello, Thanks for the picture. I dug around yesterday and think i may have found the culprit (still need to put gas in the aux tank to confirm). The connector in this picture is connected to both orange wires coming from the tanks. As i attempted to insure good connections, I found that the male connector coming out of the rubber boot felt as though it was broken. i cut that green wire and bypassed the rubber boot.
My gauge is showing about an 1/8 of a tank now. I will fill it up to see if it changes. Fingers crossed. in the past, I would run my truck on that tank until it started sputtering before switching to my main tank. Hopefully, the problem is fixed. Thanks again for your help.

20201123_155716.jpg

[alvald83]

Confirmed! That connection was the problem.

[390FE1972]

Glad to hear you got it fixed! Thanks for letting us know what worked for you.

[BigAl47]

I’m having some what the same problem. It looks like all my connections are good but it doesn’t matter if it’s on aux or main tank it just reads the main tank. Any ideas.
I have a 72 f250 sport custom 360 w/auto trans
Thanks in advance

[390FE1972]

Might be your fuel selector switch? Maybe you can test it to see if it works. Here is a link to Mac's Ford truck parts that has a replacement switch, and a thread that talks about the aux gas tank and the selector valve and switch. Hope this helps!!

http://www.fordification.com/forum/view ... =8&t=25651
https://www.macsautoparts.com/ford_truc ... -f750.html

Regards