• Welcome to ClassicBroncos! - You are currently viewing the forums as a GUEST. To take advantage of all the site features, please take a moment to register. It's fast, simple and absolutely free. So please join our community today!
    If you have problems registering or can't log into your account, please contact Admin.

1972 Bronco Alternator overcharging and battery drain.

tmeadowsalki

New Member
Joined
Oct 20, 2017
Messages
6
I have recently purchased a new alternator, voltage regulator and starter solenoid for my 1972 Bronco with a new 302. I may have wired something wrong. I am getting 14-16 volts at my battery and aftermarket voltmeter. My stock in dash gauge goes negative when revving . When I let my rig sit for more than 20 minutes the battery goes dead, n the back of the alternator there are 3 connections but i was told to leave the black terminal empty. Any ideas?
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,355
If it goes dead that fast, it sounds like either the new (and old?) alternator is bad, or you have power to the regulator all the time which is keeping the alternator energized and draining the battery. Those are about the only things that I can think of that can drain a battery that fast.

How is it wired at the regulator?
How is it wired at the alternator?

You should have three wires on the regulator's "FSAI" terminals. The "I" terminal in our case is unused.
A '72 would only have had two connections at the alternator (three if you include the ground) so that seems correct.
One of them would be the larger post with the red insulator and that is your Black w/yellow stripe wire (the largest of the wires) while the next one is for the Orange "field" wire. I can't remember the color of the insulator, but luckily they're usually marked clearly on the case of the alternator.
The main one with the Black wire is your BAT terminal, the Orange one is the FLD terminal, and the small metal tab that sticks out the side of the rubber molded strain relief of the harness connects to one of the case studs. Usually the one or two marked GRD are not convenient so it's attached to one of the others. But it must be attached.
The other end of that tab is the small Black wire that attaches to the mounting screw of the voltage regulator.

Is this how yours is connected?
For testing the regulator connector, with the regulator bolted to the body and the battery connected, pull the 4-position connector off of the regulator and test the wires. The Orange should have no power, the Yellow should have full battery voltage all the time and the Green w/red should have battery power with the key in the ON position only.
When the key is OFF you should have zero voltage at the Green wire. Make sure that this is the case.

paul
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,355
Oh, and don't throw away the old parts just yet!
New parts can be as bad, or worse than the old ones they replace. So never throw anything away until you confirm for a fact that it was in fact bad. The worst offenders are Ford starter starter relays/solenoids. With voltage regulators not far behind.
Most of the alternators end up being good, but not 100% of the time. It's not unheard of for someone to get two, three, four or even more defective starter relays in a row. Yes, it's that bad!

Was the charging system doing this before you changed the parts? What was the reason for changing them in the first place?

Paul
 
OP
OP
T

tmeadowsalki

New Member
Joined
Oct 20, 2017
Messages
6
If it goes dead that fast, it sounds like either the new (and old?) alternator is bad, or you have power to the regulator all the time which is keeping the alternator energized and draining the battery. Those are about the only things that I can think of that can drain a battery that fast.

How is it wired at the regulator?
How is it wired at the alternator?

You should have three wires on the regulator's "FSAI" terminals. The "I" terminal in our case is unused.
A '72 would only have had two connections at the alternator (three if you include the ground) so that seems correct.
One of them would be the larger post with the red insulator and that is your Black w/yellow stripe wire (the largest of the wires) while the next one is for the Orange "field" wire. I can't remember the color of the insulator, but luckily they're usually marked clearly on the case of the alternator.
The main one with the Black wire is your BAT terminal, the Orange one is the FLD terminal, and the small metal tab that sticks out the side of the rubber molded strain relief of the harness connects to one of the case studs. Usually the one or two marked GRD are not convenient so it's attached to one of the others. But it must be attached.
The other end of that tab is the small Black wire that attaches to the mounting screw of the voltage regulator.

Is this how yours is connected?
For testing the regulator connector, with the regulator bolted to the body and the battery connected, pull the 4-position connector off of the regulator and test the wires. The Orange should have no power, the Yellow should have full battery voltage all the time and the Green w/red should have battery power with the key in the ON position only.
When the key is OFF you should have zero voltage at the Green wire. Make sure that this is the case.

paul
Thanks so much!! I will try these ideas. I replaced the alternator because it was bad and that seemed to fix things for a while. I have a new Cen Tech wiring harness that has confused things and maybe the voltage regulator got wired wrong. I did add a ground wire to the back of the alternator recently to no effect. The in dash alternator gauge going backwards makes me me wonder and why the battery is get 14-16 volts makes me think it is the voltage regulator.
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
Make sure the voltage regulator is bolted to the firewall to good clean metal the voltage regulator must have good clean ground at its mounting bolts make sure you have good clean ground from the negative post of the battery to the body sheet metal by the battery. make sure your negative post ground from the battery to the engine block are clean and tight.
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
Just why did you feel the need to change the alternator and the voltage regulator. what was the failure?
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,355
And FYI, 14-15 volts is mui bueno. And mucho goodo too!
An alternator charges at typically an average of 14.5v or so. So yes, the 16v is too high and indicative of a problem if it goes on longer than just a couple of minutes, but any lower than that and you're in the normal range.

Post up a pic of your regulator wiring and we can take a look at it for you. Luckily the Centech is designed for keeping a stock alternator system, just like Painless is. Whereas some of the other custom harnesses are geared more towards other setups, including a common recommendation of a "1-wire" alternator.

Since you have a stock ammeter still, try some more tests.
With the key OFF, turn on some loads like headlights and hazard flashers. Does the gauge go lower, or higher?
Since when wiring with a new harness there is a 50/50 chance of getting it right (and therefore a 90% chance of getting it wrong!) it's easy to wire the ammeter backwards because the method of installation and lack of directional marking on the wire.
The new harnesses are geared towards eliminating the ammeter and installing a volt-meter, but leave it up to the installer.

Paul
 
OP
OP
T

tmeadowsalki

New Member
Joined
Oct 20, 2017
Messages
6
Thanks so much!! I will try these ideas. I replaced the alternator because it was bad and that seemed to fix things for a while. I have a new Cen Tech wiring harness that has confused things and maybe the voltage regulator got wired wrong. I did add a ground wire to the back of the alternator recently to no effect. The in dash alternator gauge going backwards makes me me wonder and why the battery is get 14-16 volts makes me think it is the voltage regulator.
Can I test the back of the alternator and if so what voltage should I expect?
 
OP
OP
T

tmeadowsalki

New Member
Joined
Oct 20, 2017
Messages
6
Just why did you feel the need to change the alternator and the voltage regulator. what was the failure?
The Alternator was bad and once replaced it ran great for several months. Then the battery drain startrd so I replaced the Voltage regulator and then the starter solenoid to no avail.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,355
Just FYI, the starter relay/solenoid has absolutely zero to do with the alternator and charging system. It's only jobs are:
1. Energizing the starter
2. Acting as a convenient power distribution point
3. Giving a secondary boost to the ignition coil on old-school ignitions.
4. Reducing the electrical load on the ignition switch.

The alternator output wire does connect to the battery there, but it's a direct connection so the relay is acting only in it's capacity as a distribution point. The red battery cable and black charge wire are physically connected, so the relay is nothing more than a common mounting point so they can touch.

For testing the alternator, IF you can get a test probe on to the back while the engine is running (this would probably be a bad idea from an OSHA standpoint!) you want to see that same 14-15 volts.
If all of your wiring is good, the voltage you see at the battery, at the Black charge wire on the starter relay, the back of the alternator and anywhere else you test should be the same.
Or at least within a volt of the same. Frankly, any more than a 1/2v drop at different places deserves a second look.

In the reverse of that test, with the engine OFF you should see battery voltage on the BAT post and Black w/yellow wire at the back of the alternator. It's a 10ga direct connection to the battery, so should have that same less-than-half-volt drop between what you measure at the battery with the engine off and what you measure at the back of the alternator. Less drop is better and that 10ga wire should give you full battery voltage I would think.

Paul
 
Last edited:
OP
OP
T

tmeadowsalki

New Member
Joined
Oct 20, 2017
Messages
6
ould have battery power with the key in the ON position only.
When the key is OFF you should have zero voltage at the Green wire. Make sure that this is the case.
hi Paul, the orange at the voltage regulator has poer about 15 .8 and the green has the same and the yellow . i only have one ground on the alternator tied to the engine block and the the other is untethered.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,355
Is that with the wires disconnected from the regulator, or still connected?
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,355
If disconnected then something is either crossed in the wiring or the alternator is defective.

If connected then it could be the regulator is defective, or somehow the ignition switch is sending power over the green wire.

And as we found out many times over the recent years, brand new parts are often defective.
If not immediately, then within a very short time.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,355
Also, did you verify that the wires were properly installed on the back of the alternator? Orange to the one marked FLD and black to the one marked BAT?

Is there a metal tab holding the wires in place attached to one of the studs on the back of the alternator?
 
Top