Low Voltage Issue

[EastcoastMike]

My Bronco runs and starts fine, but the voltage is consistently low. It never gets to 12V, nor does it drop below 11.2ish. Very little change in voltage whether its running or not. I only noticed because I installed a USB outlet that has a volt meter built in. I confirmed voltage with a meter.

Any ideas what is causing this?

So far I've done the following trying to chase down the issue:
1. Replaced alternator.
2. Replaced Voltage Regulator
3. cleaned all contact points for battery ground wire.
4. Asked myself why I'm so concerned if it starts and runs every time I ask it to.

Battery tested good, but only had 11v. Truck has a Centech wiring harness.

There's no voltage drop-off after sitting for a week or two. Help me out, I'm stumped.

 

[DirtDonk]

That is strange. At some point eventually it should fail to crank the engine. And by most charts, that 11v is dead as a doornail and should not crank the starter.
Do you still have a factory ammeter in the dash? What does it read?

So you should test your hand-held volt-meter on another known good setup first. Just to be sure.
With the engine running you should see 14.5v pretty consistently. Then check a known good 1.5v battery to see if it reads 1.56v or so. These two tests would pretty much tell you your meter is fine at various DC voltages. Heck, you could even test your house wiring if you wanted. Set it to AC and look for 110-125 (depending on your house and the neighborhood wiring I suppose) volts and you're good.

How many times have you started it, and how far have you driven since you noticed this? You really should only get a few starts and runs out of a battery that's not being charged.

Once you know the volt-meter is good, test the three wires at the regulator plug.
The Yellow should have the same voltage as the battery. Exactly with any luck, but at the very least within a couple of tenths of a volt.
The Green w/red wire should have 12v on it when the key is in the ON position.
The Orange wire should be tested with a voltage drop test. Lots of people around here know how to do that but I would have a hard time explaining it.

Next, with the plug still disconnected from the regulator, jumper the Orange and Yellow wires together with the engine running. As soon as you make the connection you should hear the engine bog down slightly under the load of the alternator and your voltage should jump fairly rapidly to 15, then up to 17 and maybe a bit more.
This is called "full fielding" and is a test usually done to see how much amperage the alternator is capable of developing. But without an ammeter you don't need to know that as much as watching the voltage. You can run over to the driver's side and look at your factory ammeter if you still have one, and it should read well into the +30a range. Hopefully all the way pegged if you have a 50-60 amp alternator.

If it passes this test then it would still be a good idea to find out why all your readings otherwise show low. But at least you know it's capable of charging the battery while you're driving.
If it's all accurate and you're still only getting 12v while running, then I'd have to think that eventually your battery is going to die.
Try driving it around the neighborhood with the lights on and see if that makes a difference.

In fact, turn everything on and measure voltage again to see what happens. A good alternator can maintain the desired voltage even with everything running.

Good luck

Paul

 

[gr8scott]

What year Bronco? Stock alternator? You install the Centech harness, or you buy it that way? Has it ever gone above 12 volts while running?

Try running a temporary jumper wire from bat negative (or a known GOOD ground) to the regulator case, and see if running voltage goes up.

Here's the Centech instructions if you don't already have them.
https://www.tomsbroncoparts.com/pages/wp-content/uploads/2011/12/Centech-Complete-Instructions.pdf


EDIT: Paul beat me to it, as usual

 

[EastcoastMike]

Wow, great info. Much appreciated. It’s a 70. The previous owner installed the harness, but I went through a bunch of it over the winter and it looks like he did a pretty good job on installation.

I’ve been aware of the issue for a few months- First I thought it was my USB port voltmeter. It’s just a cheap unit from amazon. I assumed it was wrong because I’ve been driving it weekly without issue. Last week I tested with a voltmeter (It’s actually a test light with a volt meter built in. I haven’t tested with a multimeter yet). and the voltage readings matched.

I didn’t realize the regulator needed to be grounded, but that makes sense. I doubt it’s getting a good ground through the mounting bolts. I’ll check that first and move on to the other suggestions.

Thanks so much for all the info!

 

[DirtDonk]

Not only do both the regulator and the alternator need to be grounded (the alternator through the engine block and the regulator through the body) but they also need to be grounded together with a small "interlink" of sorts, to maintain the same ground potential I think it's termed.
The factory harness includes a small ground wire between the alternator case and one of the mounting screws for the alternator. If you don't have that, you might want to add one.

Might be other things going on here (yet to be determined) but at least those things get you started from a proper footing.

Paul

 

[CA650]

This is Déjà vu for me.
I never did sort out what was wrong - I will say that I was really surprised how long and for how many starts you can run a bronco without a working alternator.. I ran for two weeks never noticed any problem with starts.. blinkers were a little dim and stop lights and the bluetooth AMP didn't operate because in my Bronco that amp senses the voltage and only turns itself on when voltage is above 13v.

So - i'm not much help to you on debugging this issue except to say I went through 2 alternators and my suspicion is that I fried the regulator or something during the swaps..

In the end Paul and gr8cott walked me through a one wire alternator upgrade and I pulled out the regulator entirely.. its so nice not to be thinking about that anymore.
If you're in there already... might want to consider it. Couldn't be any easier to do, although i did manage to hose it up a little anyway.

 

[EastcoastMike]

I just swapped out a complete MSD setup for a GM HEI style alternator because the MSD wasn't consistent with the timing light. Now I wonder if the issue with that setup was low voltage all along.

I grounded the body of the regulator directly to the battery. There was no change- steady at 11.6V (confirmed with an actual multi-meter). Its got to be charging because the voltage hasn't decreased in months. I'm going to have to go through DirtDonk's troubleshooting tips tonight after work.

I hate to keep adding GM parts, but if I can't figure this out, I'll go with that option. Did the GM alternator bolt right in or did you need to replace/modify the bracket?

 

[DirtDonk]

You do not need to go GM on the 1-wire setups anymore. We have a Ford 3G 1-wire version, which is what CA650 used.
You can also opt for a standard Ford 3G that still needs the other two wires connected if you're not averse to that.

Paul

 

[gr8scott]

And yes, the Ford 3G alternator is a direct bolt-in.

 

[Broncobowsher]

Don't forget to question the volt meter as well. They can be defective like any other part. I once had one that was off by 8. 8 what? whatever you measured the last digit was 8 high. Put it on 1000V AC scale and measure the wall outlet, 120V read 128V. 2V scale and 100mV read 108mV. It was a fairly nice meter, but it was the fault. I actually kept using it for about another year just correcting the readings once I knew what it was.

I've also seen meters read bad when the internal battery gets low.

 

[EastcoastMike]

Alright following Dirtdonk's instructions, here's what i found this evening:

1. Checked the yellow wire at the regulator- same voltage as battery.
2. No voltage at green wire.
3. Nothing happens when I jump the yellow to orange when running- no voltage change.
4. Since I had no voltage at the green wire, I jumped it with a small test lead- the lead wire instantly got red hot. Out of fear of frying something, i didn't proceed.

Also- confirmed my volt meter was accurate with a multimeter.

Is my next step to order the 1 wire alternator and charging cable? I really appreciate all the help and detailed info. This is a great forum.

 

[clintonvillian]

Just FYI....

I've been sorting the wires out on mine, checking all the connections with my multimeter. The only time I've seen over 12v is going across the battery terminals. Everywhere else ranges from 11.2-11.7 consistently.

I've convinced myself it's due to poor corroded grounds.

 

[Slednut10]

Just double checking- was the key in the on position when you measured 0 volts on the green w/red wire? If so, that in it self is an issue. That wire is the turn on signal for your regulator.

 

[DirtDonk]

What Slednut said. If the Green w/red wire has no reading with the key ON (but not when OFF or in ACC) then there is an issue that needs to be addressed.
However, your full-fielding test yielded bad results too.

First, find where the voltage stops on the Green w/red wire. It comes straight from the ignition switch out to the voltage regulator and, depending on what year your bronco is (sorry I forgot) may be the only wire on that circuit.

The lack of charge when jumping the yellow to the orange is a problem.
See if you can test the Orange wire to make sure it's in good contact with the FLD terminal of the back of the alternator. Not uncommon for the back of the alternators to be wired incorrectly.

Just in case:
1. Black w/yellow wire to the BAT terminal with the red insulator.
2. Orange wire to the FLD terminal with the white(?) or black(?) insulator.
3. (if '73 or later Bronco) White w/black wire to the STA terminal with (white or black?) insulator.
4. Black ground wire to one of the case studs. This is done through the metal mounting ring sticking out of the side of the black rubber strain relief.

Connections at regulator:
1. F - Orange field wire.
2. S - Green w/red switched 12v.
3. A - Yellow 12v constant wire. (plus a second Yellow wire to a radio noise suppressor if installed)
4. I - this position is not used on a Bronco.

Verify your two components have the correct connections and make sure that the Orange wire is intact.

Paul

 

[DirtDonk]

4. Since I had no voltage at the green wire, I jumped it with a small test lead- the lead wire instantly got red hot. Out of fear of frying something, i didn't proceed.

Ok, let's get some clarification here.
The test lead came from the battery directly? Positive or negative?
And you connected it to what part of the Green w/red wire? At the tip, inside the connector? Or somewhere else?
And your test wire is what got hot, or the Green w/red wire?
What gauge was the test jumper?

Thanks

Paul

 

[gr8scott]

Hey Paul, his PO installed a Centech harness. They (almost) use the same color scheme that ford
did in the charging circuit. I don't remember connecting anything to the STA terminal.

 

[EastcoastMike]

I really appreciate all your help on this. Thanks for not giving up on me yet! I answered your questions in caps, below:

Ok, let's get some clarification here.
The test lead came from the battery directly? Positive or negative?- BATTERY POSITIVE TERMINAL.

And you connected it to what part of the Green w/red wire? At the tip, inside the connector? Or somewhere else? - I JUMPED IT DIRECTLY TO THE TAB ON THE BACK OF THE VOLTAGE REGULATOR. I ALSO HAD ANOTHER TEST LEAD GROUNDING THE REGULATOR BODY TO THE BATTERY.

And your test wire is what got hot, or the Green w/red wire? THE TEST LEAD GOT HOT.

What gauge was the test jumper? IT WAS HARBOR FREIGHT'S FINEST. THE WIRE GAUGE IS PRETTY SMALL. NOT SURE WHAT SIZE IT IS THOUGH.

Thanks

Paul

 

[DirtDonk]

I don't remember connecting anything to the STA terminal.

The only thing they ever used the stator for on the Broncos was for the electric choke starting in '73.
On vehicles without an ammeter they used all four positions of the voltage regulator connector and the "S" terminal is connected to the STA stud on the alternator.
In fact, that's what it stands for. F for field, S for stator, A for armature, and I for indicator (or ignition) for the dash light.
On ammeter equipped rigs like the Bronco though, it was not used until the electric chokes came about.

The test lead came from the battery directly? Positive or negative?- BATTERY POSITIVE TERMINAL.

- I JUMPED IT DIRECTLY TO THE TAB ON THE BACK OF THE VOLTAGE REGULATOR. I ALSO HAD ANOTHER TEST LEAD GROUNDING THE REGULATOR BODY TO THE BATTERY.

THE TEST LEAD GOT HOT.

Not good. Which tab on the back of the regulator? You mean the S tab next to the others? Or something else? Some regulators do actually have an extra tab on the backside, but it's invisible unless you're looking at the back, and you don't want to be doing that since you can burn out an regulator by connecting it to power before it's grounded to the body.

We need to figure this part out.

What gauge was the test jumper? IT WAS HARBOR FREIGHT'S FINEST. THE WIRE GAUGE IS PRETTY SMALL. NOT SURE WHAT SIZE IT IS THOUGH.

Hah! Yeah, their finest indeed. But it should still be enough. Even 22ga wire should not have gotten hot and started to overheat.
Something going on there.

So, still not acting like a normal setup. When you jumpered 12v to the Orange field wire your engine speed should have bogged down some under the load of the alternator and your voltage should have jumped to above 17v or so even.

I say pull the alternator back off to verify the connections are in their proper locations and that their quality/condition is still good.

Then find out why the wire got hot. That usually means a short-circuit to ground and that's not right with a regulator.

Paul

 

[CA650]

Is my next step to order the 1 wire alternator and charging cable? I really appreciate all the help and detailed info. This is a great forum.

For me I think it was worth it, it bolted right in but Paul suggested running two v-belts instead of just one.. I had a pretty stock belt setup. only power steering, water pump and alternator with two belts.

when I put the new one-wire alternator in I put a two groove pulley on the alternator and then swapped both belts - if you do go that route I posted in that thread the size of the belts I used.

also if you do go that route your gauge in the cab should be a voltage gauge not an amp gauge. I already had an updated classic instruments style main gauge cluster that reads volts not amps.

Good luck
Mike

 

[EastcoastMike]

Ok, I think we're narrowing this down. I decided to check the regulator wires again tonight- regulator unplugged. Same results as last time, and no variation with key on or off. Yellow hot, Green and orange dead. I should have checked this last time, but I decided to hook the test light to the positive terminal- both green and orange were hot- i.e. they're both grounded with ignition on or off. The stud on the alternator for the orange wire also tests as a ground, even with the orange wire disconnected.

I grounded the old alt. Just to test it- the same lug is dead when tested.

I'm slammed this week with work. Hopefully this weekend I'll be able to put some time into this and get it sorted out. Im thinking the issue was in the green wire- then by Coincidence, I got a bad alternator. Sound possible?

If I don’t get it sorted out this weekend, I’ll be ordering that 1 wire alternator.