Hey Folks great page!

Anyways, new guy hear... and I've got a problem with the charging system on a 1975 F250 390.

The problem started out slow, notice the truck cranking over a little hard, if I started it too often, it'd run down the battery. So, I replaced the battery. This seemed to help for a while. Then I started thinking altenator. Checked voltage at battery with engine running and lights on and I was only getting about 12.2v, and would gradual fall.

So I replaced the altenator. I had the guy bench test the altenator before I installed it, tested good. Anyway, new altenator did help, still around 12v with engine running.

Next I replaced the ground wire from the battery and checked the wire harness connections from the altenator to the regulator, and replaced the regulator. On this truck, the altenator sits tight about against the block. I noticed the rvt cap on field terminal was damaged, damaged to the point that it appeared the field terminal on the altenator was ground to the engine block. The area on the engine block directly behind the Field stud on the altenator was bright white, and grease/grim free.

So, a little at a loss. Now I'm thinking battery again. I used a small 6v/12v battery charger to charge the battery for a few days and I'm thinking maybe I'm not getting a full charge on the battery. So I bought a new 80amp Schmacher charger and it's been charging for about 3 hours and still not quite there yet.

Sorry for the long winded email. Any suggestions would be appreciated!

Chad from Red Wing MN

 

Have the regulator tested. You should have at least 13.2 volts at idle with lights and heater on.

In an ideal world you'll want around 14-14.5 volts at all times, but the original Ford 1G is very inefficient. So if I saw 13.2 at idle and around 14 at 2000 RPM I wouldn't sweat it.

But, if the alternator is testing good and you're only getting 12 at the battery, either the regulator is toast or a fusible link is blown not allowing the full voltage to reach and charge the battery.

Josh

 

Try changing the positive battery cable (btwn the battery & solenoid) and cleaning all contacts. Sometimes corrosion will wick down into under the cable's insulation where it cannot be seen or inspected.

 

I have also installed some extra ground wires on my truck. One good heavy (same size as the positive battery cable) one from the block to the frame and one 12 Guage from the frame to the body. I had a problem with dim headlights and not charging all the time. I noticed that when I would step on the clutch the headlights would get brighter and the amp guage would move. The ground wires fixed the problem.

 

Thanks for the replies, i'll take another look. One thing I forgot to mention was that one test I did was I put a jumper wire on the + terminal on the altenator. To ground, I only got about 12v with the truck running and lights ongoing, with a multimeter to a ground . I tried two altenators and had them both tested, they were good. The store has a good reputation too, so i'm so I believe its not the problem.

Thanks again for the help!

Chad from Red Wing MN

 

Oh, forgot to mention. I did replace the stock regulator.

 

Have you tried checking the ground at the regulator? Try running a jumper wire from one of the regulator mounting bolts to clean, unpainted metal on the engine. If the voltage goes up, this indicates that the inner fender is not properly grounded.

 

Hey Folks,
Well, I've got a nice little vacation, so I'm hoping to get my truck's charging system working again.

I think I have a cause of the problem. Before I started monkeying around, I made sure my battery was fully charged. With the truck off, I disconnect the negative clamp from the negative terminal battery and checked voltage between the clamp and terminal and got a reading of about 12.6 volts. Shouldn't this be zero? I'm thinking this indicates a short somewhere so I started disconnecting harnesses and finallly when I disconnected the regulator harness, the voltage went to zero. My question is should the "F" terminal on the regulator harness show continuity to ground? When I removed the altenator (with the wires still attached, I noticed the I lost continuity between the "F" connector on the regulator harness and ground?

I should mention that I inspected most wires and did find a few cracked wires which I replaced.

Any help would be appreciated.

 

Just a little update. I was double checking wires and found a very degraded wire to the oil sensor. I did notice the oil pressure gauge was not working. I was referencing an oil shop manual and they mentioned that on some models, the oil sensor circut can act to "excite" the generator to charge. I didn't have time to replace the wire to the oil pressure switch, but could this be the root cause. Can anyone explain the relationship to the oil sensor on my '75 ford? Merry Christmas ya'll!

 

I just had a similar problem. Alternator was good, battery was good. Just wasn't getting anything over 12V on both battery and alternator. Didn't think it was the Regulator because it was recently replaced.
Did some research on regulators. Make sure when the key is in RUN, you should have 12V coming from the I terminal wire, and if you do you should have 12V coming out of the F terminal as well. If you don't have 12V coming out of the F terminal, the regulator is bad. Atleast that's what I read.
I wasn't getting anything out of the F terminal when I tested it this morning. Replaced the regulator and now my truck is charging better than ever.

 

The battery has a permanent connection to both the alternator and the regulator. However, current should NOT flow from the battery through the alternator because of the rectification diodes in the alternator. When the truck is OFF, current should not flow through the voltage regulator because it is DISCONNECTED inside by the field relay. As such, when the truck is shut off, there should be NO path for current out of the battery, through the charging system.

Yes, there is a path to ground here through the rotor windings of the alternator. However, the field terminal should not have any power with the truck OFF. The regulator has two sources of power: keyed power, and constant power. Keyed power is applied to the I terminal (through the ALT light in the ALT light setup) or the S terminal (ammeter setup). With an ammeter setup, applying keyed power to the S terminal of the regulator closes the field relay in the regulator. With an ALT light setup, the alternator turning (having been excited by power at the F terminal, itself sourced through the I terminal) closes the field relay. Closing the field relay applies constant power to the regulator. Constant power should have NO path to the rest of the regulator unless the field relay closes.

Based on your description, it sounds like there is a short in the regulator itself. Remove the connector from the regulator and test continuity between the I and A terminals of the regulator. There should be NO continuity. If there is, then the regulator is BAD. If there is no continuity, I would still have the regulator tested as Josh suggested because there could be another short path in the regulator. They can come bad out of the box. However, I don't know what the store tester looks for, so even if it "tests" fine I would still be inclined to exchange the regulator, personally.

Nope. There are two ways the alternator is "excited" on these era Fords:

(1) If you have an ALT light, power applied to the I terminal through the ALT light initially powers the field terminal. Power at the field terminal is what brings the alternator online ("excited"). Once the alternator begins turning, it applies power at the stator terminal (S terminal of the regulator). This closes a field relay in the regulator, which jumps the A terminal to the I terminal inside the regulator and shuts off the ALT light. Normal charging begins.

(2) If you do not have an ALT light but instead have an ammeter, keyed power is applied directly to the S terminal. The field relay is closed as soon as you turn the key to RUN, jumps the A and I terminals internally, and brings the alternator online by powering the field terminal. Once again, normal charging begins.

In either case, the oil pressure sending unit circuit is completely isolated from the regulator circuit on your truck.

 

28 AM
Good evening boys and girls sorry to hijack the feed but I am
​​​​​​ having a recurring charging system nightmare .I have an 86 F-150 4.9 so far I have replaced the alternator, battery, both alternator plugs both battery terminal cables,starter, fender mounted starter relay and I have checked all charging system wires for continuity. The alternator has an internal voltage regulator and it was new with the alternator.

The alternator has worked intermittently but the strangest part to me is that if I disconnect the positive terminal the engine runs smoother, squealing from the belt goes away and the alternator works perfectly. Also when the alternator is functioning under normal running condition the engine does the same thing. Please help I think I'm loosing my mind

Thanks
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