Technical Wiring help needed: voltage regulator/alternator

I went ahead with a 351W swap in my '51 Ford F-5 truck. Had a 239 Flathead prior with a 12V conversion. I left the wiring as it was, but hooked the appropriate wires to the Ford style alternator, and now it's charging at 16.7 volts! I figured the older, smaller, 3 prong voltage regulator was the problem, so I wired in a more modern, electronic Ford style, 4-prong regulator. Same thing is occurring; over 16 volts is going to the battery. I plan on testing another alternator from a running/driving car, but at the same time, it's possible I've not wired everything correctly as the old regulator was not marked. If you've done this before, please lend me some advice, or perhaps a diagram of how you've wired yours. I'd especially like to know which wires are what on the old regulator. Thanks in advance.

 

There's two ways to wire the older Ford alternators with the four-connection regulator; with an idiot light, and without. As your old truck won't have the light, you want the latter method...

At the alternator, connect the 'field' terminal to the 'F' terminal on the regulator.
Again at the alternator, connect the 'BAT' terminal to the battery side of your starter solenoid. If you're running an ammeter, it installs in series in this wire. If you're using a voltmeter, disregard this.
There is NO connection at the 'stator' terminal on the alternator.
At the regulator, connect the 'A' terminal to the solenoid, same place as the 'BAT' from the alternator.
Again at the regulator, connect the 'S' terminal to a SWITCHED 12V source, this should be 'hot' ONLY when the ignition switch is in the 'run' position, NOT in the 'accessory' position.
There will be NO wire connected to the 'I' terminal at the regulator.
Now, you may find a switched 12V on one of the existing regulator terminals, if so as long as it meets the above check, you can connect the 'S' terminal there rather than running all the way to the switch, using it just as a junction point. Disconnect any other wires on the existing regulator and tape them up.

DO install a separate ground wire between the alternator housing and the regulator base; this is important, and may be part of your problem if it's not there.

 

The most common issue with overcharging is A wire not getting a full voltage connection to tell the regulator what voltage to charge at...if the regulator had a bad ground when you installed it, the regulator may be blown...


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Thank you Crazy Steve for your instruction. My biggest issue is understanding where the previous alternator wires are supposed to go with the new alternator setup. It was a 12V conversion so the PO used what I think is a GM style alt that has the single battery wire post and the two tab connections at the top. There were two wires. They're all wrapped up in tape but can I assume the heavy battery wire goes back to the starter solenoid and should hook directly to the bat post on the new alternator? And the smaller wire, is that the switched 12V source I'm looking for to connect at the regulator S terminal? I did ground the regulator before installing any other wires and made sure it was a good ground direct to the inner fender metal, paint was wire-wheeled off.

 

Are the tabs vertical or horizontal....square plug or flat plug?


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The alternator used with the flathead prior to the engine swap has the single batt post out of the back and the two vertical prongs off the top/back. There's no existing plug, just the two loose wires. The thicker wire went to the batt post and I think the other wire, 10-12 gauge, went to one of the vertical tabs. Correct me if I'm wrong but this alternator is the GM or Delco style that's internally regulated? So maybe I'm overthinking things and need to get a Ford alternator with the GM internals, hook up those two existing wires and be on my way? What I thought was an existing external voltage regulator turns out to be the horn relay. My ignorance has been exposed...

 

That's where that wire should go, but I'd verify that it does go directly to the battery or solenoid.

If you had a GM three wire alternator that may be the wire you need. Again, verify that it's switched 12V and is connected to the 'ignition' terminal on your ignition switch. This wire should have 12V when the ignition switch is in the 'run' position ONLY, not in the 'ACC' or 'OFF' position. If that's NOT where it connects, you'll need to run a wire to that terminal from the regulator 'S' terminal.

You still need to run a separate ground wire between the alternator housing and the regulator base. Grounding both to chassis ground DOES NOT guarantee a near-zero ohm ground path between the two and that's what you must have.

 

The F terminal from the regulator goes to the F terminal on the alternator...looking at the back of the alternator that would be the right hand terminal. At the regulator the switched power goes to S and constant full battery voltage goes to A.


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What I don't have is any switched power going to the S terminal on the regulator. I have the S terminal connected to the STA terminal on the alternator. Most of the diagrams I've seen show it this way, but sounds like there's a few different ways of doing it, so I'll try it this way and see what we get.

 

Make the jumper wire long.... GM alternator needs the light to work.....
a photo of your setup would help

 

I don’t believe he is using this type of alternator...he is using a 10DN alternator that does not have the regulator built in and thus does not need the light...


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My understanding is he's using a late '60s/70s/80s externally regulated Ford alternator.

Maybe some pics are in order....

 

External regulated Delco alternator with Ford Regulator...


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The electrical equivalent of fruit salad... Start over with all Ford or all Delco. AND make sure that the regular is specified for the alternator that you use.

 

Why? The Ford regulator is far better than the Delco and will work with no issues...


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Pure unadulterated ignorance on my part.

 

My 35 years in the auto electric industry say differently...


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Update: All wiring completed per the instructions from Crazy Steve and others. Unfortunately I'm still getting 16.7 or so volts at the alternator batt post and over 16 volts at the battery itself. I've got another alternator I'll try; I suppose the old one I'm using could be bad? Or maybe the regulator is bad out of the box. Am I missing something else? Are there any other voltage tests I can do elsewhere that might help? Thanks guys.

 

The “A” has to have full time full battery voltage tested with a multimeter...if this has been done then something is defective for sure...


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Just for giggles...pull the field wire off the back of the alternator and then confirm that the voltage drops to battery voltage...


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Ok, even so he'll still only have three connections to the alternator; the 'F' terminals on both the alternator and regulator tie together, the 'Bat' terminal goes to the battery, and there needs to be a ground wire between the alternator case and the regulator base. The 'A' and 'S' terminals on the regulator wire the way I originally said. If it's still not working and is wired right, the regulator is bad.

 

I have seen alternators with shorted rotors that full field themselves...that is why I suggested pulling the field terminal wire on the alternator to determine if that was the issue before condemning the regulator. If the voltage drops to battery voltage and wiring is correct then the regulator is bad.


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So we're all on the same page... I'm attempting to wire up a Ford type alternator in addition to an external Ford regulator. Before my recent engine swap, the truck WAS running a GM/Delco? style 3-wire setup, internally regulated.

Explanation of my wiring: I have a ground from alternator ground post to regulator case through one of the mounting holes. I've wired a Field connection between the alternator "FLD" post and regulator "F" post. At the alternator "BATT" post I have a constant voltage battery wire feeding that one. The "S" terminal on the regulator has a verified switched power source that is hot only when the ignition key is on. And finally at the regulator "A" post I have another constant hot source coming from the starter solenoid. The "I" terminal at the regulator is not used.

Does anybody see any problems here? I'll swap alternators and report back...

 

I'll give it a go with the field wire disconnected before I swap units.

 

Are you sure your voltmeter is accurate?

 

I'm surprised this wasn't asked sooner. I think it's good, though I haven't cross-checked with another meter. I've tested it on multiple batteries in various states of charge and it's been correct.

 

With the Field wire disconnected, voltage indeed drops to battery voltage; 12.16 at alternator Batt post and 12.27 at the battery itself. So... bad regulator then???

 

Yep.... Your wiring is correct, so it must be a bad regulator.

 

I agree...don’t attach the wires to the regulator until it is mounted and grounded or you will blow the new regulator...


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Copy that. Replacement regulator in-hand. Once I finish chasing my two-year old around the neighborhood, I'll test it out and report back.