# Which one is alternator output connection at starter relay?

#### RonD

##### Well-Known Member
What was your Battery Voltage key OFF?
12.8v to 12.3volts is expected but must test it after engine has been off for at least 4 hours, overnight is better

Battery voltage has a "false" higher voltage just after charging, alternator charges the battery

If your battery voltage was under 12.2volts that could explain the 14.9volts at idle
But if you raise RPMs to say 1,500-2,000 the 14.9v should stay the same NOT go up above 15volts
If they do then yes voltage regulator is bad

just a quick "how it works"
The voltage regulator sends 7 to 9 volts to the Rotor inside alternator
The engine spins the rotor and that 7-9 volts generates 13.5v to 14.9volts in the 3 Field coils in the alternators case, that voltage comes out on B+

So the spinning of the alternator multiplies the voltage sent to the Rotor

The Voltage regulator adjusts the 7 to 9volts based on "push back" in the vehicles electrical demands
(extra credit, look up electromotive force)

"Push back" is basically how much "force" it takes to push electricity thru a circuit, once a light bulb is on it becomes harder to "push" more power thru that light bulb, there is resistance that "pushes back" on more voltage/amps coming in

When you start the engine the starter motor uses about 50AMPs of battery power
So "push back" at the battery is low because it was drained a bit, so voltage regulator sends a bit more voltage to the rotor, and voltage is above 14volts, usually 14.5-14.8volts
(and this is where a failing battery comes in, 12.2v or lower means it has very little AMPs left so very little "push back" and voltage regulator sends full 9volts to rotor)

As the battery is re-charged it starts to "push back" so voltage regulator lowers the voltage going to Rotor and voltage drops to under 14volts, 13.5 to 13.8volts is expected

The vehicles electric system also have "push back", say with lights off and heater fan off the engine and cab are using 30amps of power
When you turn on the head lights, "push back" gets less because 10 more amps are needed, so voltage regular sends more volts to Rotor
Same with heater fan on HIGH, need more amps so voltage regulator response

And then there are engine RPMs, "push back" is the same at 0MPH or at 60MPH so the voltage regulator also needs to responded to that
As the RPMs go up the Rotor creates more AMPs/Voltage, but "push back" is the same, so voltage regulator must lower the voltage it is sending to the Rotor to match the "push back"
So another sign of failing alternator is if voltage goes up with RPMs and stays UP, it WILL go up momentarily when you REV the engine but should drop back down under 14volts if you hold RPM at say 2,000rpms

Its a very simple system and easy to diagnose if you don't over think it

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#### Paisano

##### Member
I'l take a couple more readings with the multi meter in the morning, Then I'll report back

#### Paisano

##### Member
Last night I drove it long enough to get a full charge, I got 14.68 volts idling.

This morning I got

OFF....Lights off.....12.62 Volts
OFF....Lights on......12.28 Volts

#### Paisano

##### Member
I just ordered a plug-and-play new alternator(not a remanufactured one) online. I'll have to wait a few a days for it.

I picked up a new alternator here in town. When I got home, I discovered the main power connector was permanently affixed. I was kind of pissed off actually. It's the same model as the old one. But they changed the design so that you're forced to crimp or solder in a new connector. I don't like that. My truck is so old and it had multiple alternator pigtails soldered in. And every time you do that, the vehicle wire bundle gets shorter, I don't want to mess with soldering in another connector. And the plug-and-play connector I soldered in several years ago is ok to reuse.I checked it.

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#### Paisano

##### Member
Hey Guys. Thanks again, I'll follow up when the new alternator is installed.

#### Paisano

##### Member
Damn. The alternator I ordered online isn't plug-n-play like they said it was. I don't think any of the brands are anymore for my make/model. Already got it refunded.

I'm replacing just the voltage regulator instead. I got the alternator brushes on standby also, in case the old ones are worn.

Do I really need to remove the alternator to install the new voltage regulator? The alternator is at the top of the engine bay, and there should be enough room to work with the alt in place. My latest Chilton manual says be careful when installing, to make sure the brushes don't hang up on the rotor. Is this why they say remove the alternator first?

#### RonD

##### Well-Known Member
Never worked on an alternator "in the vehicle"

Usually just 2 bolts to remove with the old V belt style, in yours its 3 bolts and easy peasy, so just pull it out, and DISCONNECT either battery cable from battery FIRST, regardless

#### Paisano

##### Member
Ok. I'll remove it then. Sorry I didn't respond sooner. I'm out of Internet data till my plan renews on the 17th. So I have to find other PC's to borrow. I'm currently watching online videos on alternator brush replacement.

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#### Paisano

##### Member
I replaced the voltage regulator and alternator brushes this weekend. I opted for the complete brush holder assembly because I didn't want to bother with seating the brushes and springs in the holder. You're right, it was easy. And now I know something more about the internal workings of an alternator.

But one of the plastic retaining clips that plugs in the alternator power pigtail connector broke off. I only soldered it on a few years ago. So I fastened it on with the one remaining clip and I used a cable tie on it also. These plastic pigtail connector clips piss me off no end. These things inevitably break. Honestly, there should be a law against this. I don't think it's good to tear into your wire bundles every time you turn around to crimp or solder in new connectors. I remember many years ago, these clips were metal.

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#### ericbphoto

##### Overlander in development
Forum Moderator
Supporting Member
U.S. Military - Veteran
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You're right. Never heard Fred complain about that.

#### Paisano

##### Member
Don't get me wrong. I'm glad I learned about automotive electrical, multi-meter use, soldering and crimping. But I don't like needlessly tearing into wire harnesses, especially on an old vehicle like mine. Every time you do that, you shorten the truck wire bundle a little more.

#### RobbieD

##### Well-Known Member
Maybe it'll help the next time, but if only the plastic connector is bad or broken, and the wires and terminals are still good, on most connectors you can swap just the plastic.

Typically, there's a wedge that's removed from the connector:

And then you just pry the lock tab away and pull the wire and terminal out:

Transfer one wire at a time, matching the positions old to new.

Transferring the plastic connector from a replacement pigtail harness, to still-good wires and terminals in the truck, is a lot cleaner repair than cutting and splicing wires. Next time you're going to use a pigtail harness, check the new and the old closely, to see if you can just swap the plastic.

Main thing is, you got it fixed, and learned new skills, so you did good.

#### Paisano

##### Member
Thanks Robbie, Very interesting. I did not know this. I'll try this for next time.

After work tonight, I'll post a photo of the improvised fix which I would like to make a change to.

#### tw205

##### Bronco II Rancher.
Supporting Member
U.S. Military - Veteran
What was your Battery Voltage key OFF?
12.8v to 12.3volts is expected but must test it after engine has been off for at least 4 hours, overnight is better

Battery voltage has a "false" higher voltage just after charging, alternator charges the battery

If your battery voltage was under 12.2volts that could explain the 14.9volts at idle
But if you raise RPMs to say 1,500-2,000 the 14.9v should stay the same NOT go up above 15volts
If they do then yes voltage regulator is bad

just a quick "how it works"
The voltage regulator sends 7 to 9 volts to the Rotor inside alternator
The engine spins the rotor and that 7-9 volts generates 13.5v to 14.9volts in the 3 Field coils in the alternators case, that voltage comes out on B+

So the spinning of the alternator multiplies the voltage sent to the Rotor

The Voltage regulator adjusts the 7 to 9volts based on "push back" in the vehicles electrical demands
(extra credit, look up electromotive force)

"Push back" is basically how much "force" it takes to push electricity thru a circuit, once a light bulb is on it becomes harder to "push" more power thru that light bulb, there is resistance that "pushes back" on more voltage/amps coming in

When you start the engine the starter motor uses about 50AMPs of battery power
So "push back" at the battery is low because it was drained a bit, so voltage regulator sends a bit more voltage to the rotor, and voltage is above 14volts, usually 14.5-14.8volts
(and this is where a failing battery comes in, 12.2v or lower means it has very little AMPs left so very little "push back" and voltage regulator sends full 9volts to rotor)

As the battery is re-charged it starts to "push back" so voltage regulator lowers the voltage going to Rotor and voltage drops to under 14volts, 13.5 to 13.8volts is expected

The vehicles electric system also have "push back", say with lights off and heater fan off the engine and cab are using 30amps of power
When you turn on the head lights, "push back" gets less because 10 more amps are needed, so voltage regular sends more volts to Rotor
Same with heater fan on HIGH, need more amps so voltage regulator response

And then there are engine RPMs, "push back" is the same at 0MPH or at 60MPH so the voltage regulator also needs to responded to that
As the RPMs go up the Rotor creates more AMPs/Voltage, but "push back" is the same, so voltage regulator must lower the voltage it is sending to the Rotor to match the "push back"
So another sign of failing alternator is if voltage goes up with RPMs and stays UP, it WILL go up momentarily when you REV the engine but should drop back down under 14volts if you hold RPM at say 2,000rpms

Its a very simple system and easy to diagnose if you don't over think it
Great info!!! So I have an 89 BII that recently needed a new battery. When I start I get 14.89v but it never goes below 14.54 even after a 20 mile run. Would that be voltage reg or computer? Thanks.

#### RonD

##### Well-Known Member
Great info!!! So I have an 89 BII that recently needed a new battery. When I start I get 14.89v but it never goes below 14.54 even after a 20 mile run. Would that be voltage reg or computer? Thanks.
What's the battery voltage key OFF?

Just after startup Voltage regulator will use +2volts, so 12.8v battery would see 14.8volt

After a few minutes voltage regulator should drop it down to +1volt, so 13.8volt

There is not an actual "number" the voltage regulator uses "push back" voltage/AMPs
Just after starting, the battery is drained so low "push back"
As battery gets recharged "push back" goes up so voltage regulator lowers voltage, actually AMPs, but in this case you measure the voltage

When you turn on all the lights "push back" in the system drops a bit so voltage regulator increases the AMPs, so you would see a voltage drop and then voltage would come back up once the lights were on, so AMPs were increased to match system "push back"

The Yellow wire on voltage regulator reads the "push back" in the system, I would test that it reads EXACTLY battery voltage with Key OFF
If it reads a little less then there is corrosion in that wire or at is connection to battery, which can be a fuse or fusible link
The corrosion cause low "push back" all the time so higher voltage all the time, which is bad for the battery, but it makes the lights brighter, lol

You can do this test after engine has been running for at least 10min
Engine on
Lights off
Heater fan off or Low
Test battery voltage, lets say it is 14.2volts
Turn on all the lights, turn fan to HIGH
test battery volts
Should still be 14.2volts
If its lower, like 13.9volts then voltage regulator is "stuck", its not adjusting voltage/amp output to the system

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