Stock grounding wire locations

[FoMoCoBronCo]

Need some help identifying grounding wires + locations in my mostly original ‘71 w/ C4+302.

I didn’t take enough photographs of the wiring during disassembly and it’s biting me in the @ss.

Currently, the only grounding wire hooked up is running from my negative battery terminal to my engine block (it’s not pictured).

I am left with the three wires that are pictured. Here’s what I know:

Wire 1: This is a wire that is original to the bronco, and still has its original insulation. However, the 1 or both of the ends might have been replaced at some point. The 2nd photograph attached to this post shows that one end of it was hooked to a grounding block on the body. I don’t know where the other end hooked up to.

Wire 2: this is an aftermarket wire labeled 8 Gauge, 600V. It was hooked up at the same point on the body as wire one. I also don’t know where the other end hooked up to.

Wire 3: this is also an original wire. All of the original insulation was cracked and flaked off, so I wrapped it in Tesa tape. I don’t have a photograph of its location prior to disassembly; however, it looks similar to other photos I have seen of the wire that runs between the engine block (mounted to the same bolt as the battery ground wire) and the inner fender around the corner from the starter relay.

I believe from my research that this year bronco came stock with a grounding wire from the battery to the block, the block to the body, and the battery to the body. if anyone could give me some guidance or post photos of their Broncos stock wiring locations, I would be greatly appreciative!

 

[Oldtimer]

The "grounding block" in photo 2 is actually a battery isolator diode block.
Alternator power would have connected to middle terminal of isolator.
One end of isolator went to stock batter, other end went to second battery.
Isolater power in went out to both batteries, but diodes kept one battery from draining other when running accessories with out alternator charging.

Stock ground wires would have been battery to block, a bolt at front passenger corner of block near oil pan.
From same bolt was a ground wire that split, with one end going to alternator case, and other end to mounting bolt for regulator.
EDIT: On my 68, there is also a ground wire from block bolt to starter relay mounting bolt.
I wouold also add a ground wire from battery to body (passenger fender), and one from the core support to body ground.

 

[FoMoCoBronCo]

The "grounding block" in photo 2 is actually a battery isolator diode block.
Alternator power would have connected to middle terminal of isolator.
One end of isolator went to stock batter, other end went to second battery.
Isolater power in went out to both batteries, but diodes kept one battery from draining other when running accessories with out alternator charging.

Stock ground wires would have been battery to block, a bolt at front passenger corner of block near oil pan.
From same bolt was a ground wire that split, with one end going to alternator case, and other end to mounting bolt for regulator.
I wouold also add a ground wire from battery to body (passenger fender), and one from the core support to body ground.

View attachment 916213

Wow, thank you! That is some great information. I wonder if the “stock” grounding wire locations varied year to year. My 1971 has a grounding wire that runs between the alternator housing and the regulator body bolt; it is wrapped in the harness with the other wires between the alternator and the voltage regulator. (you can see where it attaches to the alternator in the first picture.)

The second picture is of a grounding wire I stole off my ‘72 Parts bronco. It is original and has two ground wires running off of one end in parallel. I have seen people mention that this wire would have run off the negative battery terminal to the block, then the smaller parallel wire from the block to the inner fender wall, around the corner from the starter relay. (As in the 3rd picture I attached)

But the Parts bronco, I stole it off of had this grounding wire running from a valve cover bolt to the passenger side body (at the inner/outer fender connection bolt), with the smaller wire running to the aforementioned spot on the inner fender. I’m not sure if this was the stock set up, or if the PO of the parts bronco rearranged it that way.

Then I’ve got the way you described that’s in the picture you included. I’m probably splitting hairs, but I like to keep things as close to stock where possible, to make things easier for myself, and any future owners.

Sent from my iPhone using Tapatalk

 

[Oldtimer]

If you are running EFI, a lot of people recommend an added ground wire from back of intake manifold to body (firewall).

 

[DirtDonk]

As far as I know, all years of early Bronco use the same grounding scheme with regard to the Main and Alternator grounds.
That one you show in the last picture, that’s obviously been destroyed, that’s still bolted to the body, is the original negative battery ground cable that grounded both the body and the engine.
What most people thought of as an anchor clamp on the inner wheel well, was actually the body ground.
To my knowledge they stayed the same from 66 to 77.

Same for the Alternator, where the ground was buried in the molded rubber strain relief and harness and ran up to the external voltage regulator mounting bolt.

Although I’ve heard of some existing, I’ve never seen a separate ground wire or strap between the back of the engine and the firewall, on an EB.
During the time the Broncos were made, Ford was already doing that on passenger cars and full-size trucks. But I’ve never seen one even on a 77.
Although there are a couple of members here, who say that their 77’s did come with one.
So maybe it was a running change.

 

[bronco italiano]

You cannot have enough grounds on an EB.