G3 Alternator in 1975 5.0 Bronco - Engine Won't Shut Off

[Lawson]

Will replace DVM battery and test again. I am feeling rather embarrassed, confused? If I cut the orange wire before and it didn't kill the engine, when would the engine shut off now, unless I made some mistake in reporting the original symptom of the engine continuing to run with the ignition OFF. Maybe the ignition was ON? Does thus push me towards a diode as a solution? Will retest and post results.

 

[Lawson]

Ok, a new battery in the DVM changed things just a bit....

- Base battery reading 12.65V
- Will truck start with orange cut? Yes.
- What is the battery reading at with engine running? 14.44
- Will the truck shut off? Yes

So with no orange wire connected, it would appear the system is charging.

With engine off volts on battery now read 12.83.

So the battery took some charge, was charging while the engine was running, and shut off. Tell me why I need that orange wire again? And if it is charging, is it being regulated in some way, or just getting blasted with a full charge by the alternator?

About .45 volts running through the orange wire with the truck running.
The orange wire has 12.37 with key in RUN position, but engine off.
Battery voltage with engine running for about 10 minutes right about 14.v with the headlights on.
About 14.2 with lights off.

I there any reason that I can't put in my new battery? I didn't want to rush into it since my old battery was working.

 

[DirtDonk]

If I cut the orange wire before and it didn't kill the engine, when would the engine shut off now, unless I made some mistake in reporting the original symptom of the engine continuing to run with the ignition OFF.

Because as we mentioned awhile back (and the whole reason for this test in fact), perhaps the alternator was charging anyway, once it was started. And as it turns out, that's not only the case but you in fact have what appears to be a self-exciting ("1-wire") GM alternator.
So not only is the Orange wire apparently not needed for the alternator to charge, but was in fact feeding back to the ignition switch, back through the Red w/green wire (maybe) which is (again maybe) probably being used to give the engine harness it's "switched" power.

Maybe the ignition was ON? Does thus push me towards a diode as a solution? Will retest and post results.

Yes. Or just disconnect the Orange wire and leave it disconnected since it apparently is not needed from your next post.

Paul

 

[DirtDonk]

- Base battery reading 12.65V

No problem there. Battery sounds fully charged.

- Will truck start with orange cut? Yes.

Which is expected. The Orange wire, and the entire alternator circuit has nothing to do with the starter. It was the shutting down that we were curious about, but it's at least good to know that nothing seems to be shorted through the two separate circuits.

- What is the battery reading at with engine running? 14.44

Sort of excellent. At least we know the alternator is charging perfectly. But we now also know that it fires up on it's own without the Orange wire.
Leading us to believe that you in fact have a true 1-wire alternator instead of what was sold to you. Or, it might have been sold that way and the wire, as also suspected earlier, is for a non-ammeter Ford wiring setup just to illuminate a dash lamp. Not to be excited by, but to simply light the lamp.
Which you don't have.

- Will the truck shut off? Yes

Bingo! And hallelujah! Leave it and move on.
Disconnect the Green w/red from the Orange wire, remove the orange wire and don't try to use it unless you want a dash light. Hmm, which might not be a bad idea I suppose.

Paul

 

[DirtDonk]

AT least that's what I think, based on my minimal knowledge of GM alternators.
But if it works...%)

Paul

 

[Lawson]

Disconnect the Green w/red from the Orange wire, remove the orange wire and don't try to use it unless you want a dash light. Hmm, which might not be a bad idea I suppose.

Hmmm. One little caveat. When I start the truck, the red light next to my key does light up. Aren't you saying that shouldn't happen? Or that if my alternator has problems in the future, I won't get that light. I'm good with either. I just want to make sure that leaving that disconnected isn't doing to harm anything, or over-charge the battery or some such thing.

Leading us to believe that you in fact have a true 1-wire alternator instead of what was sold to you. Or, it might have been sold that way and the wire, as also suspected earlier, is for a non-ammeter Ford wiring setup just to illuminate a dash lamp. Not to be excited by, but to simply light the lamp.

7278F-6-135A-3 WIRE-12SI PLUG-SP - Given the part number of the alternator, it would appear to be a 3 wire....

Now about that non-ammeter Ford wiring setup, you are out of my depth on that comment. I'm wading pretty shallow as it is, but let me make this possibly embarrassing statement. Are you saying that this alternator was for a 66-77 Bronco as advertised, with 66-77 wiring, but since my vehicle is a "hybrid" using a 1990 Ford Mustang harness and electronics, the 66-77 rules don't apply?

I'll buy that? Why not, after all, it's working and I have to get packed and ready for a trip! I just don't want a battery bomb to go off as I saunter down the highway. I'm confused in how a battery charges, or knows when to charge, or how it doesn't overcharge. But hey, who would question a gentleman with the name of DirtDonk? Lol

 

[DirtDonk]

Hmmm. One little caveat. When I start the truck, the red light next to my key does light up.

You mean the one marked "BRAKE" by any chance?

Aren't you saying that shouldn't happen?

Don't know. If its the BRAKE warning lamp, it's exactly as it should happen. Only during start does it self-test, then goes back out. If it comes on while driving, you have a leak or other imbalance in your brake system between the front and rear lines.

Or that if my alternator has problems in the future, I won't get that light.

Let's see the light first.

I'm good with either. I just want to make sure that leaving that disconnected isn't doing to harm anything, or over-charge the battery or some such thing.

It's not so far, from your testing. That 14-something volts is just right. You should always see between 13.5 and 14.5 (or within a couple of tenths of those) when the engine is running. When it goes above or below that is when you need to get to digging for trouble. A volt gauge in your cluster or on your dash somewhere else is a necessity with your setup. Or a light.
There are aftermarket digital gauges that simply plug into the cigarette lighter that let you monitor your voltage at a glance. Very cool actually.
There are also similar ones you drill a hole for, for a more permanent mount.
I'm not aware of any harm in leaving the one wire disconnected if everything is working. But again, not being a GM alternator person, hopefully someone will join the conversation that is and can tell us both.

7278F-6-135A-3 WIRE-12SI PLUG-SP - Given the part number of the alternator, it would appear to be a 3 wire....

Yeah, but here again it might be that we're not on the same page as the GM engineers. Maybe that third wire is not needed for anything but the dash indicator lamp. That we don't have...
If it's needed for telling the alternator to turn on and charge, well, it seems to not be working and you should call the seller for clarification.
If it's only needed for the light, then you should not have any trouble. But carry your newly powered up volt-meter with you!
This way you can sneak a test in now and then when you stop for gas and your family is none the wiser. Or upset about how much attention you're paying to your Bronco!

Now about that non-ammeter Ford wiring setup, you are out of my depth on that comment. I'm wading pretty shallow as it is, but let me make this possibly embarrassing statement. Are you saying that this alternator was for a 66-77 Bronco as advertised, with 66-77 wiring...

Don't know for sure. Maybe they (the seller) just isn't aware of the difference in regulator wiring in Broncos. Would not be the first time.

...but since my vehicle is a "hybrid" using a 1990 Ford Mustang harness and electronics, the 66-77 rules don't apply?

Nope. Not at all. The engine harness is always separate entity from the chassis/body harness, and can work with anything. We just always have to differentiate between the two. But in the case of the charging system, it's usually at least considered mostly to the body side. They just happen to sometimes have a common connector. IN our EFI harness we have an alternator exciter wire (the infamous Green w/red!) already built in to the engine harness. That's just to keep things clean though, and so you don't have to run your own. It still plugs into the stock body harness behind the engine, but is taped up in the engine harness for cleanliness.

By "non-ammeter" I was referring to something that Ford themselves did. Some Ford vehicles (cars and trucks) use lights only. While others (such as all Early Broncos) use gauges and no lights at all. So while a Mustang of a certain year, or a pickup truck of a particular option package, might have just a battery/charge indicator light, we have an ammeter.
In the two cases, the voltage regulator is wired completely different! Even most shop mechanics don't know, or don't remember that. We've seen many a shop mis-wire the regulator because they were more versed in standard Fords, and may never have even worked on one with an ammeter and the different wiring scheme.
So we have our 3-wire regulator harnesses, and they have their 4-wire regulator harnesses. And never the twain shall meet...

I'll buy that? Why not, after all, it's working and I have to get packed and ready for a trip! I just don't want a battery bomb to go off as I saunter down the highway. I'm confused in how a battery charges, or knows when to charge, or how it doesn't overcharge. But hey, who would question a gentleman with the name of DirtDonk? Lol

Haha! Get to packing there guy!

 

[Lawson]

Thanks again for all the help. I'll get back to the seller and see if they have anything to add to the discussion. Lesson? Buy from someone that knows early Broncos and their systems. If I learn anything interesting I'll pass it along.