Hello All,

I have spent the afternoon and evening looking on FTE, Search engine and last but certainly not least garysgaragemahal websites and found nothing. So i bring my quest to the brain trust for the answers i seek. Those who know me know i do my best to exhaust all resources before i clutter our beloved FTE.

After my my fuel gauge and cigarette plug stopped working i figured that the G701 must be the culprit.

I am looking for a picture and a fomoco diagram of the elusive location G701 ground point. I know it should be near the right side of the radio. Since i have no radio i thought it might make locationing it easier but alas not as of yet.

While digging around in the void that once housed a deluxe vintage am push button fomoco radio i did find a single black (circled) wire with a blue stripe. I tried grounding it with the engine running with no responses from the cigarette plug or the fuel gauge.

The picture also contains a splice i made when i eliminated the midship fuel tank. The gauge and the cigarette plug both had power for the last several years with no issues.

I am seeking a picture of the grounding point location and or picture of a fomoco service manual grounding point location.

Thank you all in advance.

 

First I hope you checked the black / blue wire for power before sending it to ground?

My under standing on that ground is it is seen / gotten to from the bottom up, I think you might be up to high?
My truck dose not have that ground even if the books all say it should.
And I should know as I had 2 81 trucks apart to swap harnesses.

With a test light have you checked if the lighter is getting power to it think on the yellow wire?
I want to say the ground is to the outside barrel but cant remember if there is a ground wire on it or not at this time?
If there is a wire maybe you can trace it to ground?

On the fuel gauge I would ground the wire at the sender and see if the gauge moves or if you use a test light it should blink.

I would pull all the fuses and put a meter to them as some times they look good but are not.
Some of them do have a way to test when installed but I still pull them.
Its strange that they both stopped at the same time as they dont get power from the same place and I cant see the ground being it but maybe?
Again I would check for power first then the other side for each.

Just thinking here there are a few grounds on the firewall in the engine bay by the wiper motor would not hurt to check / clean them.
Good luck
Dave ----

 

Here's a picture. Remember in the picture below, you are looking at the backside of the instrument panel, like you have x-ray vision through the firewall. This ground is not the most common problem that causes a fuel gauge not to work. I don't remember a thread with your story on that.

 

P.S. Black with a ightblue stripe feeds the courtesy light circuit.

 

The subject truck is an '85, originally a diesel. Not sure what year or model you posted, but here's the index for the entire EVTM:

https://www.garysgaragemahal.com/1985-evtm.html


The dash illustration looks pretty much the same:




I'm going to jump on the bandwagon that G701 is likely NOT at fault. In the EVTM, look at page 7 (diesel grounds) to see how many circuits pass through this single point:




If G701 was loose from the dash, all of those circuits would be inop. Unless everything on that page was dead, I wouldn't even bother trying to find G701.

For the lighter's ground, look at splice S162 in the diagram above. Five circuits are grounded through S162. If the wire from there to G701 was broken, those other four items would also be dead. Here's the diagram for the lighter circuit, page 112. The same fuse powers the horn and the lighter, via splice S221. If the horn works, you know the fuse and circuit is good at least to S221:








Fuel gauge here, page 110. This gets a little convoluted, as the truck has been converted from two tanks to one. Note how the fuel tank sender has two grounds, G701 and G105. Even if G701 was completely disconnected, the circuit should still work just fine with only G105. Also look at the ground circuits again on page 7 above. The tank sender reaches ground via splice S154. Look how many other items are also grounded through this splice. If those circuits are working properly, you know at least that portion of that big diagram is good.







Troubleshooting for the gauges here, page 111:





Rather than trying to get to the sender for initial troubleshooting (must drop tank), I'd suggest trying connector C127 because access is so much easier. See figure 1 on page 97. C127 is near the brake master cylinder. You can measure the resistance through the sender to ground, etc., all from this connector. Careful, because C127 is shown in two spots in the diagram above, but the wires are physically adjacent. This connector carries the signal between the gauge and sender (illustrated just below the instrument cluster), and also the ground from the sender to G701 and G105 (illustrated just below the sender:




If it's just killing you not knowing exactly where G701 is located, you can still test it without having to physically touch it. Look at the ground for the lighter, on pages 7 and 112 above. This ground wire is connected to the outer shell of the lighter socket. You can easily access this wire and run a test jumper from there to a known good ground. If somehow G701 had worked loose or had otherwise failed, grounding this wire would now ground everything seen on page 7. See if anything changes. You can also check continuity to ground from this wire, to make sure G701 is well grounded and the circuit is intact.

 

Right in the middle of page 84. Even if the optional lights were never installed, the harness is still there. Make sure your dome light still works. If not, you probably blew fuse #8:

 

Hi Dave,

I unfortunately didn't check the little black wire for power before i gounded it.

This current harness is a 1980. The chassis is a diesel that was swapped before i owned ol'blue. There could have been a harness swap before i own the truck.

the behind the dash wiring swap wasn't a job i had intended on leaving alone do long and not one my grandfather would have approved of. In the middle of the harness swap a buddy called and needed help and a truck so i buttoned it up and turned a blind eye to the whole thing.

I am shifting my sat schedule around to work on this wiring bonanza uninterrupted. You know it didn't occur to me the ground might not be centered behind the dash panel.


Thanks for the suggestions!! If i do infact find the G701 i will take plenty of pictures.

Thanks for your post and incite into this issue. I will keep you and everyone else posted.

 

Hi Dave,

That is the page i have been looking for! I remember seeing it but couldn't find it. I don't remember a thread i started with this either.

if you don't mind where did you find that picture? I am sure i have seen it before.

Thanks for your time and effort in helping me fix this.

 

Hi Dave,

It's a feed wire. Wow i didn't expect that from a black wire. Thanks!!

 

Hi Karl,

ol'blue is kind of a junkyard dog. I am running a 1980 f100/f150 wiring harness. I dug around Gary's website had found that first diagram you provided.

It is a strange deal. If only the lighter and fuel gauge are effected according to the ground tree picture it wouldn't make a lot of sense. I see your point.

While i am in the dash i intend on correcting the duel fuel tank wiring as well as several other issues.

Thanks for your interest and help in repairing my problem.
I will keep you and everyone posted.

 

Hi Karl,

i don't even have the dome light wired at the moment plan to fix that and a whole host of wiring issues tomorrow. I did check the fuse and it was good. To my surprise.

Thanks again Karl. Appreciate your help.

 

Would like to thank you guys for all the information!! I will be putting it to good use starting in the morning. Will do my best to document my progress in order to help others.
shall keep everyone posted.

 

Just a mid day update. Got a late start. G701 found!


more later.

 

Update ~ well after a most of my day while daylight was on my side i pulled the top of the dash off and the center trim piece. I rooted around the area between the front on the dash and the firewall.

journeying thru the reminds me of adding the 1980 wiring harness to the passenger side 1985 wiring harness. Quite a challenging project. I can certainly reconfigure a ford gray plug if needed. I took pictures of the three plugs and assigned them identification numbers of #1, #2 and #3. I took readings from each and at what position ignition and headlight switch was at the time of being hot as well the wire colors.


Plugs #1 and #2 Plug #1 Green w/yellow st. Hot all the time, White w/purple st. Hot at run, Blue w/red st. Hot lights on and run. Black w/yellow st. Dead or ground. Plug #2 Red w/white st. Dead. Brown hot lights on in run. Black w/yellow st. Dead or ground.


Plug #3 (1980 wired plug*) Red w/yellow dots* hot in run. Red w/green st. Hot in run. Black cold or ground.

I am currently looking through my collection of wiring diagrams and internet information. Ol'blue has dash lighting and any other wiring convinces this old man needs. It should be know that there is no dome lighting or clearance lights. Never found it necessary. The door switches are connected either.

The fuel gauge is most likely the ground i will check the rest of the circuit tomorrow.

I will keep everyone posted on my progress.

 

I think you are doing this but to make sure, the main color of the wire is listed first, the stripe or hash mark color is listed second. This can be important.

Red/blue is the start circuit from the ignition switch, through a neutral safety if you have one, and then out to the starter solenoid on the fender.

Blue/red is the dash lighting and is hot only when the headlight switch is pulled half or all the way out. The blue/red is also dimmed by twisting the headlight ****. And the blue/red has it's own fuse in the fuse box.