Alternator replacement questions

[Tamnative3]

I had my alternator tested and it was bad so I go a rebuilt one installed it and when I checked it with a multimeter it showed only 12.4 volts with the truck running at about 2500 rpm. I figured that I got a bad one and took it back for a replacement and asked them To check it before I took it. He checked it while I was there and it passed so I took it home and installed it, same issue 12.4 volts.
Now I checked all the wires from the alt. to the regulator plug and all were fine, I also replaced the regulator just to make sure but I still just get low 12 v readings, am I missing somethin. Changing these is a real bi&@! and this is the 3rd time I have done it so I trying to figure out what I did. I was expecting 14.xx volts am I wrong?

 

[Broncobowsher]

What is the voltage with the engine off?
At idle?
And we know 12.4V at 2500 RPM

With the key on, engine off, what is the voltage on the STA terminal on the back of the alternator?

Probably more questions later, depends on how this first round goes.

 

[DirtDonk]

No, you are correct.
How did you check the wires to the regulator? Did you disconnect the plug and measure full battery voltage on the yellow wire? 12 V approximately on the green with red stripe wire only when the key is in the ON position?

Are you measuring voltage at the battery, or at the very back of the alternator on the BAT terminal?

Is the regulator directly grounded to the alternator via the very small black wire that has a ring terminal that fits under one of the regulator mounting bolts?

And last, but not least, do not connect the regulator to the wiring until it is securely bolted to the body and grounded via the small wire to the alternator.

 

[Tamnative3]

What is the voltage with the engine off?
At idle?
And we know 12.4V at 2500 RPM

With the key on, engine off, what is the voltage on the STA terminal on the back of the alternator?

Probably more questions later, depends on how this first round goes.

 

[Tamnative3]

Engine off 12.2
I didn’t measure the STA I don’t know if I can get to it but I’ll try

 

[Tamnative3]

No, you are correct.
How did you check the wires to the regulator? Did you disconnect the plug and measure full battery voltage on the yellow wire? 12 V approximately on the green with red stripe wire only when the key is in the ON position?

Are you measuring voltage at the battery, or at the very back of the alternator on the BAT terminal?

Is the regulator directly grounded to the alternator via the very small black wire that has a ring terminal that fits under one of the regulator mounting bolts?

And last, but not least, do not connect the regulator to the wiring until it is securely bolted to the body and grounded via the small wire to the alternator.

 

[Tamnative3]

I just did a continuity between the regulator plug and the connectors on the beck of the alt. When I had the alt. it is very difficult to get to the back of the alt. whe it’s installed .
I am measuring off the battery.
I don’t have a black wire from the reg to the alt but I checked to see if they were all grounded and the were.

 

[Tamnative3]

I also replaced the regulator and it is bolted to the firewall.

 

[DirtDonk]

Check for voltage readings on the regulator connector.
Continuity doesn’t tell you anything, or at least not much. And besides, there is literally only one wire connected between the regulator connector and the alternator. That wire is the orange FLD wire.
All the other wires are independent, except for the small ground wire. Which needs to be there for proper function by the way. It can work without it, but it works better with it.
Is this an original electrical harness, or replacement?

 

[Tamnative3]

Check for voltage readings on the regulator connector.
Continuity doesn’t tell you anything, or at least not much. And besides, there is literally only one wire connected between the regulator connector and the alternator. That wire is the orange FLD wire.
All the other wires are independent, except for the small ground wire. Which needs to be there for proper function by the way. It can work without it, but it works better with it.
Is this an original electrical harness, or replacement?

It is the original harness the plug has 4 connectors but only 3 have wires going to them the no.1 on the left has nothing but there are 4 spades coming from the regulator.

 

[Tamnative3]

What is the voltage with the engine off?
At idle?
And we know 12.4V at 2500 RPM

With the key on, engine off, what is the voltage on the STA terminal on the back of the alternator?

Probably more questions later, depends on how this first round goes.

With key on engine off the stator shows .05 volts.

Check for voltage readings on the regulator connector.
Continuity doesn’t tell you anything, or at least not much. And besides, there is literally only one wire connected between the regulator connector and the alternator. That wire is the orange FLD wire.
All the other wires are independent, except for the small ground wire. Which needs to be there for proper function by the way. It can work without it, but it works better with it.
Is this an original electrical harness, or replacement?

with key on engine not running :
FLD. 0 volts ,when wire is removed from alternator it has 5.0 ohms resistance between regulator and alternator terminal.
On alternator with no wires attached it has 5.4 ohms resistance between terminal and case.
With everything hooked up on the alt. And key on it shows 12.11 volts same as what the battery is.
It does have a ground wire from the reg. to the metal tab that attaches to the case.
Also I have read that the testing machines that they use are not that accurate. I am going To get another alt. But this one will be from America not China. Let me know what you think of the above information thanks.

 

[Viperwolf1]

0 volts on the field is a problem. You can't develop output without current at the field. Check this voltage back at the regulator F terminal. If you don't have it there, either the regulator is bad or you don't have 12V at the green-red wire to turn the regulator on.

 

[Broncobowsher]

I goofed and asked for the wrong thing, you you gave the right answer...
FLD wire at 0 volts. Field is the throttle for the alternator. The more field voltage, the more the alternator should be making. With the engine off and the key on, the voltage regulator should be calling for max output on the alternator. You should be seeing close to battery voltage. Without the engine running, there is no output to satisify the regulator for it to start backing off the charge rate (reduce the field voltage). This has to be done key because it takes power to run the field. Not much, but would otherwise run the battery down trying to get the alternator to make a charge when it isn't spinning.

At this point, I'm calling the alternator good. It just isn't getting the signal it needs to throttle up the output when running. The field is not getting energized. With the key on, what is the voltage at each of the 3 wires at the regulator? This will point to the next direction to look.

 

[Tamnative3]

What if the amp meter was wired backwards I.e. showing charge when it should be showing discharge?

 

[DirtDonk]

It is the original harness the plug has 4 connectors but only 3 have wires going to them the no.1 on the left has nothing but there are 4 spades coming from the regulator.

Correct for all Early Broncos. As well as any older Ford that utilized an ammeter in the instrument cluster, rather than a charge indicator lamp.
Labelled FSAI the "I" position is not utilized on Broncos.
Check for voltage on "S" and "A" with the wires disconnected from the regulator.

with key on engine not running :
FLD. 0 volts ,when wire is removed from alternator it has 5.0 ohms resistance between regulator and alternator terminal.
On alternator with no wires attached it has 5.4 ohms resistance between terminal and case.

The others will know if resistance tells us anything. I only check for voltage.

With everything hooked up on the alt. And key on it shows 12.11 volts same as what the battery is.

Which terminal are you measuring to get the 12.11v?

It does have a ground wire from the reg. to the metal tab that attaches to the case.

Great. Good to know it's still there.

Also I have read that the testing machines that they use are not that accurate. I am going To get another alt. But this one will be from America not China. Let me know what you think of the above information thanks.

Usually, if the test machines are good, the testing employees don't always have good training in it's use.
Why not test it yourself? With the regulator disconnected, connect a jumper wire between the "A" (Yellow) wire and the "S" (Green w/red) wire. With the engine running, you should see full output (it's called "full-fielding") and the battery might read anywhere from 15 to 18 volts or so.
Obviously, don't do this for long! Just enough to test.

Good luck finding one built in the US! Do you happen to have one of the few rebuilders in your area that knows what they're doing? Lots of them have gone by the wayside over the last 20-30 years.
Even then, the parts they have access to are usually made in, or sourced from China and elsewhere overseas. Even BBB that's built in Mexico (after they bought out many of the old US builders in the last 90's and early 00's) probably source at least some of their parts from oveseas.
But if you find one, let us all know!!!!! I'd buy them too...

Paul

 

[DirtDonk]

What if the amp meter was wired backwards I.e. showing charge when it should be showing discharge?

It could happen, but it's just reading things. It has zero effect on the actual working of the alternator.
It would simply read backwards.

Does it currently show a negative when you turn things on, like the headlights and heater?

Paul

 

[Tamnative3]

Correct for all Early Broncos. As well as any older Ford that utilized an ammeter in the instrument cluster, rather than a charge indicator lamp.
Labelled FSAI the "I" position is not utilized on Broncos.
Check for voltage on "S" and "A" with the wires disconnected from the regulator.

The others will know if resistance tells us anything. I only check for voltage.

Which terminal are you measuring to get the 12.11v?

Great. Good to know it's still there.

Usually, if the test machines are good, the testing employees don't always have good training in it's use.
Why not test it yourself? With the regulator disconnected, connect a jumper wire between the "A" (Yellow) wire and the "S" (Green w/red) wire. With the engine running, you should see full output (it's called "full-fielding") and the battery might read anywhere from 15 to 18 volts or so.
Obviously, don't do this for long! Just enough to test.

Good luck finding one built in the US! Do you happen to have one of the few rebuilders in your area that knows what they're doing? Lots of them have gone by the wayside over the last 20-30 years.
Even then, the parts they have access to are usually made in, or sourced from China and elsewhere overseas. Even BBB that's built in Mexico (after they bought out many of the old US builders in the last 90's and early 00's) probably source at least some of their parts from oveseas.
But if you find one, let us all know!!!!! I'd buy them too...

Paul

The 12.11 was taken at the batt. Terminal on the alt.

 

[Broncobowsher]

The 12.11 was taken at the batt. Terminal on the alt.

Exactly what I would expect. No load on the electrical system, voltage the same. When running and the alternator is working, I expect a little higher on the alternator due to voltage drop in the wiring. How much, depends on the alternator output.

 

[Tamnative3]

It could happen, but it's just reading things. It has zero effect on the actual working of the alternator.
It would simply read backwards.

Does it currently show a negative when you turn things on, like the headlights and heater?

Paul

No it is reading backwards

I goofed and asked for the wrong thing, you you gave the right answer...
FLD wire at 0 volts. Field is the throttle for the alternator. The more field voltage, the more the alternator should be making. With the engine off and the key on, the voltage regulator should be calling for max output on the alternator. You should be seeing close to battery voltage. Without the engine running, there is no output to satisify the regulator for it to start backing off the charge rate (reduce the field voltage). This has to be done key because it takes power to run the field. Not much, but would otherwise run the battery down trying to get the alternator to make a charge when it isn't spinning.

At this point, I'm calling the alternator good. It just isn't getting the signal it needs to throttle up the output when running. The field is not getting energized. With the key on, what is the voltage at each of the 3 wires at the regulator? This will point to the next direction to look.

At the plug I go :
S. 12.6 volts green/ red tracer
F 0v. Orange wire
A 0v. Yellow wire

 

[Broncobowsher]

I'm looking stuff up and am confused. Before you go off anything I say here, let others who know factory wiring better confirm this. I deal with too much non-stock wiring to go off color codes.
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https://painlessperformance.com/wp-content/uploads/2024/02/90527.pdf page 54 is the generic Ford external regulator wiring I reference. It gives terminal names, not wire colors.