I have a 1976 ford f-250 4x4 with a 390 and I can't seem to figure out whats wrong with the charging. I have a new alternator and regulator and brand new wiring harness. With all this new stuff I assume I wired it wrong. It is a points style ignition so it doesn't have the ignition module. I don't know if I need more grounds or what. I have all the wires hooked up to my knowledge. "F" to the field "S" to the stator and "A" to the alternator battery terminal. Can somebody please help me?

 

There is a fourth wire that's kind of hidden. It's a ground wire. On the original harness the three wires that connect to the alternator have a rubber strain relief that is held to the alternator by a metal tab, this tab is actually a ground wire that goes from the strain relief to the regulator. It connects to one of the screws of the regulator mount.
Usually the alternator will ground through the brackets but Ford apparently felt the need to add the additional ground to tie the regulator to the alternator.

 

Voltage regulator? Did you change it or check it?

 

Ok I'll check it tomorrow when I have a little time but if this doesn't solve the problem then I guess its back to the drawing boards ha ha ha.

 

I bought a new voltage regulator when I picked up the alternator because thats what I was told to do

 

What's the actual problem? So far you've only told us that there is one, and that you can't figure it out. Assuming the battery is not charging, how have you determined this? I assume some voltage measurements under various conditions? What were the results of those measurements? Or are you not even there yet? In other words, what are the actual symptoms?

 

I have a multi-meter with the battery setting and I hooked it up and the truck is running off of the battery. When the truck is off the charge reads about 12.6V when I start it up and run it the Voltage goes down slowly maybe .01V every few minutes while idling. When I hold the gas the voltage doesn't increase.

 

Definitely sounds like when the voltage regulator goes bad. You said you got a new regulator and alternator, though. I just re-read this, and you said you have a new wiring harness as well.

I am confused, as these are the only ways to not get voltage. Maybe a picture of the wiring would help?

 

Thanks for the detailed explanation. Try these things next:

1) Remove the plug from the voltage regulator. On the female plug, the connector that would go to the 'A' terminal of the regulator should have 12 volts at all times. If this truck has an ALT light in the dash, the connector that would go to the 'I' terminal should have 12 volts with the key in RUN. If this truck has an ammeter (charge gauge, amp gauge) in the dash, the 'S' terminal should have 12 volts with the key in RUN instead. However, because you said the 'S' terminal of the regulator is tied to the STA stud of the alternator, that would be indicative of an ALT light setup - if this is not the case, let me know as your wiring is wrong.

2) Take both the alternator and regulator to the store to be tested. It's very common to get a bad regulator out of the box, especially if it's a budget or value brand. When you pay for the premium brand, you're really just paying for quality control.

 

Sorry I haven't gotten back. But my truck uses the ammeter. it doesn't work, well actually none of my gauges work only the Speedometer the gauges are all broken up in the back so nothing connects. My alternator tests fine and so does the regulator. I was wondering do I need a wire that connects to the positive side of the battery or not? just a thought. But I have tried everything I know to do and I can't figure it out. The wiring matches the book so I'm not sure

 

In my last post, I told you to check certain signals coming from the regulator connector for power based on the position of the key. I cannot move forward with you until you do this.

If you have an ammeter setup, there should be NO connection between the alternator STA stud and the S terminal of the regulator. The S terminal of the regulator should get keyed power in your case. When you do what I told you to do above, we're probably going to find that your regulator is not getting powered on and therefore not bringing the alternator online because you have the system wired incorrectly. What is connected to the I terminal of the regulator?

I don't understand your question about a wire from the battery. Are you saying the charging system does not make any connection to the battery at all? Please describe the entire setup you are working with.

 

I will start with the "S" because it doesn't have keyed power it is just hooked from alternator to regulator. So I would just tap into the battery wire from the ignition. The "I" terminal doesn't have anything wired to it the book said it wasn't needed for my application. And as far as I know I don't have a wire that connects from alternator to the battery. My wiring kit didn't come with one. I'm always worried that if I wire something really wrong I'll fry everything. As far as the work I won't really be able to get anything done until either the weekend when I have time. I might have time after school to dink around with it a little but when I test everything out that you've told me I'll let you know the results

 

For an ammeter setup, this is wrong.

I'm not sure what you mean by battery wire; if you mean the hot-at-all-times input to the ignition switch from the battery, then no. You want a hot-in-RUN source which originally ran out to the regulator as a GREEN with RED stripe wire on your setup.

That's correct.

If there's no connection from the alternator to the battery, there's no way for current from the alternator to actually charge the battery. The large output stud of the alternator runs to the battery side of the starter solenoid through a fusible link and heavy gauge wire. Otherwise the alternator does nothing. This signal also needs to branch out to the 'A' terminal of the regulator (lighter gauge). This is the sense input to the regulator. To summarize:

Regulator
S: needs 12 volts with the key in RUN.
A: needs 12 volts at all times.
F: goes directly to FLD stud of the alternator.

Alternator
Large stud (BATT, B+ sometimes A): goes to the battery side of the starter solenoid through a fusible link, also branches out to the 'A' terminal of the regulator to satisfy its 12 volts at all times requirement.
STA: goes to the electric-assist choke ONLY. NO connection to the regulator.
FLD: goes directly to the 'F' input of the regulator.

Also, it's very common (and recommended) to run a small ground wire from one of the regulator mounting bolts to the GND stud on the back of the alternator, if available. Very little current flows through here; it's just to help close the regulator sense loop.

This is why it's important to do all of this work with the negative battery cable disconnected. The most important thing is to protect the alternator output with a fusible link. If you don't feel comfortable performing this work, then I respectfully advise you to have a shop do this because you're dealing with heavy currents, and you must be careful when doing anything around a battery. Good electrical craftsmanship is also important when performing this work especially.

 

Hey man thanks for all your help, everyone else I asked looked at me sideways and said I don't know. I got it charging yesterday so now I am able to use my truck again, and thanks again.