Thanks Lou. The way my '91 is set up is that the two batteries positive terminals are connected together and then one cable goes to the starter while another wire goes to the selenoid mounted on the fender wall. There is a wire that connects the selonoid to the alternator, this is the constant power supply to the alternator, there is 12.40VDC on this wire. Just to rule out the selonoid and the wire I bi-passed the two by disconnecting the wire from from the selonoid and connecting a 12 gauge wire from the positive battery terminal to the alternator. It still didn't work so I put everything back to stock.

Now there's a total of 4 wires connected to the alternator:
1) Constant Power Supply
2) Ground
3) Stator
4) Field

The Constant Power Supply is known to be good. I have not checked the ground yet. The Stator is connected to the voltage regulator scores a 0.6 on an Ohm test. The Field is connected to the voltage regulator and scores a 0.6 on an Ohm test.

What, if any, should the voltage be from the voltage regulator to both the Stator and the Field?

Thanks again,

Bart

 

There are 4 wires connected at the voltage regulator and I tested 3 of them for continuity:
I - Ignition (?)
F - Field (good continutity)
S - Stator (good continutity)
A - Alternator (good continutity)

I'm not sure about the I. Does anyone know if that stands for Ignition? And where is the other end of the wire connect to so that I can test it's continuity.

Another question, is there any dependency on the ignition switch for charging the system?

Thanks,

Bart

 

Well I finally got it working. I stopped by Checkers after work and picked up another Voltage Regulator just for fun. Turns out the one from Napa was faulty. I'm just glad my old truck is finally working! Yaaaaaaaaaaaahhhhhhhhhhhhhooooooooooooo!!!!!

Thanks for all the advice guys. I learned a lot on this one

Bart

 

Very nice

 

i am glad you got it fixed. remember just because it is new does not mean its good

 

Thanks elginitis

That sure was a hard lesson to learn, not to mention hard to stomach(2 bad parts... ). In retrospect I learned a few things:

1 - When you buy an alternator, have the shop bench test it before you leave.
2 - Don't just through parts at a problem. I guess I was hoping the problem would go away without me having to understand ALL the ins and outs of my charging system.
3 - Learn how to use a volt meter, ohm meter, and continuity tester. These tools aren't hard to use after you understand them. To an electrician it's all common sense, and since I was dealing with electricty it should of been common sense for me too. (Better late then never ).

Enjoy

bart

 

My Mantra...Stay away from discount auto parts stores and lifetime warranty electrical parts.
Everyone needs to find a reputable and respected starter/alternator specialty shop in their neighborhood. Professional rebuilders use better parts and are selling the best charging system parts you can buy.

 

You should have 14.7 volts coming off your alternator. Not 12 something. Most all professional battery charging equipment charges at a rate of 13.2, that is close to what you should have across the terminals of the battery. Between your alternator and ground, with the batteries disconnected you should have 14.7 volts, or damn close to it. Anything more will fry your batteries, anything less wont charge your batteries while your playing the radio or running lights. Your alternator is an AC (yes household current) charging device. All alts. use a diode pack to turn the AC into DC for use in motor vehicles. if you are putting out 12.5 volts and then you turn on the radio or headlights, how much voltage do you think your battery is getting now? Anyway, you should be getting more voltage than you are across the terminals of the battery, and 14.7 from the alt to ground, with the batteries disconnected. You have a short, that is draining voltage from the alternator and the batteries, probably in the voltage regulator. If its not there then I would first disconnect any after market equipment that has been installed. As you disconnect equipment watch your alternator reading, not at the battery but at the alternator. Bad cells, low electrolite, defective batteries, all can change your reading at the battery.

 

WOW - And I thought I was finished with this fix. I'll have to go back and recheck what kind of volts I'm putting out from the alternator. Thanks for the insight!

bart

 

recheck all your voltages and make sure you have over 14 volts. try this start the truck and turn on everything(lights heater etc) and measure your voltage drop. it should be about 1 volt. lets see how your alt performs under a load. i learned this when i had trouble and the alt was fine with no load, but turn on everything and voltage went down to 9.x volts. hope this helps

 

OK I have been following this thread because I have the exact same problem. I have been through three alternators adn Ican't believe it has been a bad atlernator everytime. The truck charges fine with no load but when a big load is placed on the system then everything dims and slows down. I think I may just take it to a electric shop and see what they say. But I would really like to fix it my self. If the voltage readings are low under a heavy load what do I do then?

 

I have repeated this info many times, I hope to save some people the same aggravation I went thru. I put 6 or 7 second generation alternators into my 92 F150 from Nov 95 till Fall 2003. My original alternator went bad, I replaced it with a Pep Boys "lifetime warranty" alt. Each alternator died after less than a year or so average. The bearings would usually be shot, the rectifier would short circuit, and I would be stuck. I went off to Pep Boys time and time again to take advantage of the so-called warranty. Then one day I got smart, I went to a professional starter and alternator rebuilder in my town. He told me the second gen alt is a poor choice even when it is functioning and that I would be better off with the Ford 3rd gen. He also said that buying parts from Pep Boys was your first mistake.

If you have a second gen alt, you will notice an external fan under the pulley and two plastic plugs for the wiring connectors. The third gen has a smaller pulley,internal fan, and one connector and the other wires go to studs.

Any second gen alternator can be removed and replaced with a third gen. The bracket is exactly the same, some wires have to be cut and moved but that is all.
Never put a second generation alt. on your truck again.

Do not buy alternators from discount auto stores!!! You will get stranded!!!

 

I used to work for Pep Boys. It's what you are buying. A "Lifetime Alternator" means rebuilt. Ask for a new part, not rebuilt. You are buying a warranty, not a new alternator. When you buy a 5 year battery, as apposed to a 2 year battery, do you think the extra money is buying you a "Super BAttery"? Your paying extra for 3 years added to a warranty. The battery is the same. Juma35, dont forget your alternator is designed to charge at a running RPM, not at idle.

 

Just to add to this thread a bit.

You replaced both the alt and the voltage regulator for a second time AFTER discovering and replacing the shredded positive battery wire. It is more likely that the wire, while grounding out, took out both of the new parts, rather than them being faulty. It never hurts to check all main wires in the charging system, and replace if they even look questionable. Installing some wire loom around them is just added protection, as well.

 

RR4E - I hadn't really thought about that. You're probably right about the voltage regulator... I bet I fried it with the shredded positve cable. But I wonder about the alternator. Both the alternator and the voltage regulator were replaced before the cable got shredded and it still wasn't charging. So there are a couple scenarios that could be true:

1 - both the VR and the alternator were bad before I shredded the cable
2 - the VR was bad before I shredded the cable and the alternator was fine
3 - the alternator was bad before I shredded the able the VR was fine

Could it of been possible that both the VR and the alternator were working properly befor eI shredded the cable?

bart