77 Chassis Wiring Harness Diagram

[msommer001]

Does anyone have the chassis wiring harness for the 1977 ranger with 2 tanks.

I replaced the chassis wiring harness and it appears that the fuel sending units wiring is within this harness. Looks like the previous owner wiring them with some separate wiring.

I need a diagram to verify the connections and how to undo what the PO did.

I have the diagram of the fuel selector and fuel gauge.

Thanks


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[bronkenn]

https://seabiscuit68.tripod.com/

 

[DirtDonk]

Not sure I am understanding your current dilemma.
You said you replaced the chassis harness, but if so that would’ve included every wire, including the two fuel sending units.
Yet you say there is still some PO wiring left? If you have new wiring for the fuel tanks, why not just use it?

Which harness did you use to replace the old one?
Unfortunately most diagrams will show you what is what, but they rarely, if ever show you where everything is located on the vehicle.
Do you have pictures of what you’re dealing with?

 

[sprdv1]

https://seabiscuit68.tripod.com/

Good man

 

[msommer001]

Not sure I am understanding your current dilemma.
You said you replaced the chassis harness, but if so that would’ve included every wire, including the two fuel sending units.
Yet you say there is still some PO wiring left? If you have new wiring for the fuel tanks, why not just use it?

Which harness did you use to replace the old one?
Unfortunately most diagrams will show you what is what, but they rarely, if ever show you where everything is located on the vehicle.
Do you have pictures of what you’re dealing with?

Since the PO wired the sending units outside of the harness, there are a couple of wires under that look factory that are not landed on anything. I think the PO disconnected them and run they outside the harness. Not sure why.

Here is a photo of where the new harness plugs into the old at the fire wall. I believe that orange wire is for the main tank and the yellow is for the aux tank.

Looks like an orange with a white stripe, another one the is just orange.

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[DirtDonk]

Thanks for the pic. So you didn't replace what most of us consider the chassis harness complete. You replaced a section of it, presumably down on the frame from the engine compartment to the rear lights? Whether correct or not, most of us call the entire vehicle wiring harness the "chassis" harness.
The fuel sender wires are often separated at some point because they come out at different points (front tank and rear tank) and sometimes are wrapped, sometimes not.
At the back of the cluster they are often separate from the harness because they go to the dash mounted switch to change which tank the gauge reads from.

Yes the main wire is Orange, but I have not seen one (or just don't remember) seeing a white stripe. The aux tank is Yellow with a stripe though, so you might see that at the dash switch.

Even on two-tank Broncos with the switch though, there is a "bypass" so to speak, near the switch where the Orange wire can re-connect directly to the Orange wire so that your gauge only reads off of the main tank. This will be how it is from the factory with a single tank so they did not have to have two separate harnesses for one vs two tanks.
You should see an odd-shaped 90 degree connector near the switch on the Orange wires that you can fiddle around with if the switch ever gives up the ghost on you.

And truly it does not stop anything working if you mix up the wires between the two tanks. Just makes the gauge read off of the wrong tank. Not a good thing, but easily remedied.
The Orange wire is definitely for the back tank though, with a Yellow wire for the aux tank.

Do you have the switch in easy reach so you can see what's on the back of it? Do you even have two tanks? Many of the aux tanks have been removed over the years especially when larger rear tanks were installed.

paul

 

[DirtDonk]

Sorry, now I can see the switch in your picture (now that I'm actually looking for it!) and see that there may have been some tweaks.
hard to say if it was to replace the switch with a non-stock unit, or due to busted up ends.
I seem to remember the stock one used push-on connectors and yours appears to have screw-on terminals. Maybe the ends were replaced to suit the switch, but the rest of the wires are still original?
Can you see the weird 90 degree connector anywhere?

 

[DirtDonk]

Aha! I think that's in in the picture. Looks like the switch has been bypassed for use with just the rear tank only.
Is there anything like an electric pump in use? An electric tank switching valve perhaps? Maybe some new stuff was used, or maybe the old switch just gave up the good life for retirement.

paul

 

[DirtDonk]

And sorry ahead of time if I'm missing some memories and got some of that wrong, but at least you know what some other things are that you are looking at. Might lead you to seeing what's wrong.

By the way... What's wrong? Gauge not working, or just trying to find a home for some of the new wires?

Paul

 

[msommer001]

And sorry ahead of time if I'm missing some memories and got some of that wrong, but at least you know what some other things are that you are looking at. Might lead you to seeing what's wrong.

By the way... What's wrong? Gauge not working, or just trying to find a home for some of the new wires?

Paul

The Gauge is working fine. I would like it wired correctly. Plus I seem to have an electrical short when I apply the brakes that send a crackle through the radio. So as part of fixing that I want to eliminate any old wires.

I think I might just have to take the plunge and replace it all with a new painless harness.


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[msommer001]

Aha! I think that's in in the picture. Looks like the switch has been bypassed for use with just the rear tank only.
Is there anything like an electric pump in use? An electric tank switching valve perhaps? Maybe some new stuff was used, or maybe the old switch just gave up the good life for retirement.

paul

No electrical fuel pump but yes an electrical tank selector


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[DirtDonk]

A snapping/popping sound is pretty normal when hitting the brakes. At least for older vehicles.
That doesn’t mean it’s correct, as you are thinking. But it is common.

First things first though. Verify that you have a couple of good body grounds from the battery and the engine.
The main negative battery cable should go to the engine block of course, but there should be a secondary one going to the body near the fender and starter relay.
A secondary one which Ford never installed would be from the back of the engine to the firewall. This is a good secondary path to avoid old rusty, broken or just painted surfaces.
And since I think the radio grounds to the dash, make sure the dash is well grounded to the body also.
Yes I know it’s bolted, but sometimes a little extra jumper wire between body panels can cure a lot of ills.
It could be as simple as just an old tired brake lamp switch, which happens a lot on these old trucks too, but renewing and adding grounds is a good thing to do no matter what.

 

[msommer001]

A snapping/popping sound is pretty normal when hitting the brakes. At least for older vehicles.
That doesn’t mean it’s correct, as you are thinking. But it is common.

First things first though. Verify that you have a couple of good body grounds from the battery and the engine.
The main negative battery cable should go to the engine block of course, but there should be a secondary one going to the body near the fender and starter relay.
A secondary one which Ford never installed would be from the back of the engine to the firewall. This is a good secondary path to avoid old rusty, broken or just painted surfaces.
And since I think the radio grounds to the dash, make sure the dash is well grounded to the body also.
Yes I know it’s bolted, but sometimes a little extra jumper wire between body panels can cure a lot of ills.
It could be as simple as just an old tired brake lamp switch, which happens a lot on these old trucks too, but renewing and adding grounds is a good thing to do no matter what.

In addition to the radio crackling, the headlight, brake lights and heater motors all flicker. Seems like a global issue.

I will check the grounds. I believe you also recommend a ground from the alternator to the negative battery post as well correct.

I have replaced the brake light switch but that did not mitigate the issue.

Mark


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[DirtDonk]

The brake light switch gets its power from the headlight switch. From there it goes to the tail lights via the turn signal switch.
Has a long convoluted path with lots of potential noisemakers.

Maybe it’s a lack of grounding, or maybe it’s a lack of available power.
Just to make sure everything‘s on the up and up measure your battery voltage and see where it sits naturally. Should be pretty near 12.5 V or a little above.
Next time the engine is running measure battery voltage again. Should be over 14 V.
After that check voltage at all the components we are talking about.
Check the power coming into the brake light switch and headlight switch and other things that you can access. Even the ignition switch.
What you’re looking for is voltage drop.
Make sure that you don’t have substantial voltage drop. Anything over 1 V on any of those components is notable.
Maybe not the end of the world, but definitely worth keeping in mind.

Are you running an original style alternator with a voltage regulator on the fender? If so then make sure you have a ground wire between the alternator case and one of the screws holding regulator to body.
Otherwise, an additional ground between the alternator and the battery is not a bad thing. Usually not completely necessary, but wouldn’t hurt anything and might help if your system is having a ground deficiency.

 

[sprdv1]

The Gauge is working fine. I would like it wired correctly. Plus I seem to have an electrical short when I apply the brakes that send a crackle through the radio. So as part of fixing that I want to eliminate any old wires.

I think I might just have to take the plunge and replace it all with a new painless harness.


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never hurts to upgrade

 

[sprdv1]

Otherwise, an additional ground between the alternator and the battery is not a bad thing. Usually not completely necessary, but wouldn’t hurt anything and might help if your system is having a ground deficiency.

always something w/damn wiring.. Grounds for sure won't hurt

 

[msommer001]

always something w/damn wiring.. Grounds for sure won't hurt

Ok, this weekend I am going to throw on a few grounds and make sure any that are in place now have good connections.


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[msommer001]

A huge thanks to all. I added the grounds as recommended and it resolved my electrical issue.

Thanks again,
Mark


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[Howard2x4x4]

https://seabiscuit68.tripod.com/

Wow, that's truly impressive Ken!

 

[bronkenn]

That is a nice source, Howard. That fellow put a lot of effort into it. I keep it in my files.