76 Alternator 3 wire harness

[tampabronco]

Looked at the bronco parts houses for a 76 3 alternator wire harness and can't find one specifically listed for a 76. I see one for a 66-73. Is there a difference?

 

[DirtDonk]

Yes. And there are even differences between 66 and 73, so I’m not sure how they can make one fit all of those years.
It’s mostly in the style of connectors, but there might be other minor differences as well.

How bad is yours? And how badly do you want to keep it original looking, versus just fixing what’s there?

 

[tampabronco]

Yes. And there are even differences between 66 and 73, so I’m not sure how they can make one fit all of those years.
It’s mostly in the style of connectors, but there might be other minor differences as well.

How bad is yours? And how badly do you want to keep it original looking, versus just fixing what’s there?

best I can tell the wires are good and serviceable. Upgrading the alternator to a 90 amp and wanted to upgrade the harness at the same time

 

[DirtDonk]

Then you have to make your own. You can’t utilize any of the stock replacement ones because they still utilize the entire original charge loop.
And while if everything is in perfect shape a 90 amp alternator won’t often tax the limits, it’s just too close for comfort.

So in my opinion it’s time to retire the original alternator wires and make your own. And besides, aren’t you replacing it with an internally regulated alternator? The stock replacements are all going to have external regulator wires.
Or is the harness you were referring to an upgrade style? If that’s what you meant I misunderstood.

 

[DirtDonk]

For the time being (until you say otherwise) I'll assume it's a modern internally regulated alternator you're going to be using. If that's the case, then you don't really re-use any of the old alternator harness as it will only confuse things and also be under-sized for the new higher output alternator.

So look up any of the many 3G conversion discussions here and you'll get a mess of instructions and advice. But just to add some details here, you basically want a larger gauge main BAT output wire and will run it directly to the battery positive, or positive side of the starter relay/solenoid on the fender. Best practice is to fuse it as well for protection.
Here is the one we sell for 3G conversions: https://www.wildhorses4x4.com/product/Battery_Charge_Cable_AMG_fused/Bronco_Starters
It utilizes a 6ga battery cable style conductor to handle the higher rated units, including the 130a factory style and even higher output versions.
This is the same size that Ford themselves has been using since the introduction of the 3G in 90 and 130 amp models. On some with longer runs, such as vans, or higher loads such as diesel pickup trucks, they use the larger 4ga size cable instead.
So you can make your own, or as you can see you can buy them pre-made as well. Because it's a custom retrofit, it does not matter what year your Bronco is. You're using this to replace your original harness.

Is this what you're contemplating?

Paul

 

[tampabronco]

For the time being (until you say otherwise) I'll assume it's a modern internally regulated alternator you're going to be using. If that's the case, then you don't really re-use any of the old alternator harness as it will only confuse things and also be under-sized for the new higher output alternator.

So look up any of the many 3G conversion discussions here and you'll get a mess of instructions and advice. But just to add some details here, you basically want a larger gauge main BAT output wire and will run it directly to the battery positive, or positive side of the starter relay/solenoid on the fender. Best practice is to fuse it as well for protection.
Here is the one we sell for 3G conversions: https://www.wildhorses4x4.com/product/Battery_Charge_Cable_AMG_fused/Bronco_Starters
It utilizes a 6ga battery cable style conductor to handle the higher rated units, including the 130a factory style and even higher output versions.
This is the same size that Ford themselves has been using since the introduction of the 3G in 90 and 130 amp models. On some with longer runs, such as vans, or higher loads such as diesel pickup trucks, they use the larger 4ga size cable instead.
So you can make your own, or as you can see you can buy them pre-made as well. Because it's a custom retrofit, it does not matter what year your Bronco is. You're using this to replace your original harness.

Is this what you're contemplating?

Paul

I was contemplating a 3G but found a local alternator reman shop with an reman/upgraded 90 Amp Ford 3 wire. I was thinking I could find a beefed up 3 wire harness. Finding that's not the case...

 

[DirtDonk]

No such thing unfortunately. A beefed up charge harness for a bronco is by definition a beefed up entire vehicle harness.
That’s because the alternator output runs up to the body, into the cabin, feeds all the accessories and the fuse panel, runs through the ammeter, then runs back out the firewall to charge the battery.
So there’s probably about 10 to 12 feet of that black wire and only about 12 inches of it are in the alternator-specific harness.

On that note, Centech states that their vehicle harness is capable of handling 100 amp alternators. But I would not equate that to saying that the original Ford wiring can handle that much. They use the same gauge wire, but in a different orientation. And the wire is new, not 40+ years old.

So you had the right idea. Just did not extend that enough into the rest of the system to work.

 

[DirtDonk]

You didn’t hear this from me… But if you were at the point where you must get their alternator redone and still want to go with the higher output, then it’s possible it can work for a while.

But you must be honest with yourself as to the condition of the rest of the wiring and check all the points to be sure that it is in tiptop shape, with no defects or old age issues that can hinder the flow of electrons and build up resistance and heat.
If all those conditions are met and your battery is fully charged to begin with, you might be able to make it live for a time until you upgrade the entire harness. But are you willing to take the chance?

I ran a 70 amp alternator for years on mine with never a tiny problem. Wires were in good shape and 70 A was just within the range for the systems capacity.

The very first rewire job I did was on a 69 with 100 amp alternator that decided to go wonky one morning and melt down the main charge wire. It literally took the entire wiring harness through the engine compartment and under the dash with it when it went up in smoke.

Just sayin’…

 

[DirtDonk]

Now that the PSA and warnings are over, you can still install your hundred amp alternator even with the old harness. But you must bypass the main charge wire and instead run a new one up to the battery directly.

Because the run is so short you could even still use 10 gauge wire if you wanted. Eight gauge would be even better, but 10 would be acceptable.
Run a new wire from the BAT terminal to the battery side of the starter relay, terminate the old one safely and you should be good to go.

If you’re not comfortable with Wiring, don’t go in blind. Do a lot of research and listen to a lot of other voices besides mine first.

 

[tampabronco]

Now that the PSA and warnings are over, you can still install your hundred amp alternator even with the old harness. But you must bypass the main charge wire and instead run a new one up to the battery directly.

Because the run is so short you could even still use 10 gauge wire if you wanted. Eight gauge would be even better, but 10 would be acceptable.
Run a new wire from the BAT terminal to the battery side of the starter relay, terminate the old one safely and you should be good to go.

If you’re not comfortable with Wiring, don’t go in blind. Do a lot of research and listen to a lot of other voices besides mine first.

Thanks for the advice. Wonder if I should just go with the 3G alternator upgrade at this point

 

[DirtDonk]

Up to you. Either one is a legit upgrade, with the 3G being obviously the newer design.
Is the rebuild a competitive price? Even though a 3g is usually a virtual bolt-in proposition, if the rebuild is exactly like your old one then it is a for-sure bolt-in.
The larger ford alternators tend to cause a v-belt to squeal. No experience with upgrading a stock one so don’t know if they suffer the same fate.

 

[chrlsful]

I'm at this point (plus) too. Found a 3g (dont wanna gm 1) w/180* mounts (12'n 6 o'clock) that's a mounting replacement for the oe. But I'm eliminating the inner fender starting solenoid w/a pmgr starter. Gotta fresh 4L Thriftpower, 5 speed yetah, yetah, Wanna 'smooth' all the wires in the bay'n bring in a late model fresh air tube (right over the 2 just named components. Will have THAT plus heater hoses takin up local real estate). I hope the alternator I found (not purchases yet) is a 'small case'. A finned alloy valve cover & header flange R also room hogs on that upper passenger side of the bay. I like what I'm contemplating (its 130A) as I will have 2 batteries and the CB's in the cab, winch is on the front, H4 hdlghts. Trouble IS I never followed auto electrics for understanding & just keep meeting Mr Sparky (Paul just helped me w/the grounds issue) in all the most fascinatin places.
aahahahaa
any1 know ofa small case 3G (taurus, Mark VIIIIII ) ? w/180* mounts?
Thnx !

 

[DirtDonk]

I thought the small case was not available in the 130 amp version. But I could be wrong.

I understand wanting to eliminate the original starter relay from the fender, but Ford didn’t even do it that way. Ford kept it and for good reasons.
Have you read all the stories of the people that have done it already? Are you going to add a diode to the control circuit? I think that’s the solution anyway.

 

[chrlsful]

"... a diode to the control circuit?..."
a when to the who?
sure...
doh!

 

[904Bronco]

3G small case is typically 90 amps and it will make a single V-belt squeal on occation. It puts out far more amps at a lower rpm, so more load on the V-belt.
3G large case is 130 amp, and I have seen them (aftermarket) advertised up to 200 amp. How they get it there, I don't know.
And a V-belt on a 130 amp 3G can make some noise too... There is only so much belt tightening that can go on to counteract squeal before you glaze a belt/over work a bearing.

Paul is correct, Ford starter relays on late model EFI cars, have a diode built in to prevent feedback.

There is a thread somewhere that had a long list of donar cars for both sizes of the 3G, I thought 94-95 mustangs were one of them, but it has been a while...

 

[DirtDonk]

There is another bad thing that happens when you eliminate the Ford starter relay. The typical bronco ignition switch is put under a higher load and has a higher than normal failure rate. That would be bad enough with original parts, but with modern replacement bar parts being rather cheap on the inside, it’s very possible that you won’t have a long life expectancy from the ignition switch.

A starter solenoid would tend to use a little more current than a starter relay. Puts more load on an already taxed switch.
I’ve never seen an actual back to back test to see how much current is used by each of those components, so it’s possible that the higher failure rate that we’ve seen over the years was simply coincidence.
But I’m skeptical…

 

[chrlsful]

"...How they get it there, I don't know...."
"...I’m skeptical…..."
All good news. I can get beefier components, do some hiding or - the most likely, give it over to an automotive electrics expert. A PulPal welding alternater is in the cards so it's not just confusing to me but likely - soon beyond my understanding
aahahahaa

"...a diode in the control circuit..."
"...diode built in..."
more beyond my understanding. Where would I put that in? May B it is not needed as 1 is in the alternater? But how does that help the starting subsystem after the solinoid is removed (charging v starting). Doesnt take much info in auto ele & I'm lost. I dont believe gm ever used a starting solinoid (modern or historic). Most my mopowrs hada white ceramic thing I saw ina ford or two (only) but never the other makes, & so on...I guess a lill knowledge gets one into hot water. May B a hi skol text on automotive el systems would help

 

[DirtDonk]

The problem with removing the relay on the fender when converting to the modern style PMGR starters is that when you wire them correctly there is often some short-term feedback through the system that keeps the starter running for a few seconds.
I can't remember exactly why it does this, but it happens quite often. The starter acts like a generator while it's winding down and keeps the energizing circuit energized which in turn keeps the starter spinning because it's connected directly to the battery.
The fender mounted relay acts as an isolator to stop this.

And as mentioned it also serves to reduce the load on the ignition switch. You can use any kind of a relay you wanted I would think, which would reduce the load on the switch. But you might still have to do something about the run-on issue.

Paul

 

[chrlsful]

This is good. All news to me - an electron dummy.
Whats this diode? How duz it help? Would it prevent power back load on keyed ign (a 'blow up") or starter 'run on' (something to chew up teeth)?
"...relay acts as an isolator to stop this...."
where would it go in the system (between what components)?
Sorry to hit up guys w/all the Qs. Might just B nother area my dreams? ideas? will go unfulfilled (well, always 'hieda' solenoid game to play). The pmgr starter's extra wire must go somewhere. The 3G One will go to the battery (thru maxi fuse). Dont't wanna go "too far off" that it will bea mess if putting in the welder (if I do) or other battery. May B the one area I sub out in 40yrs ownership. Guys here taught me the carb rebuild B4 Mike's hada thousand vids up (or did he say 'several thousand'). May B I stepped on tampa's thread too heavy? Time to start nother thread? Whadda ya say OP?

 

[904Bronco]

A diode is a one way road, power flows one way through it and cannot travel back... No feedback.