Charging Issues on a 72

[Skitzo]

Hey guys, I have an issue I need some opinions on. I have searched through the site and didn't find was I was looking for so I'm throwing this out there for some help diagnosing this. I have a 72 with a 302. The battery will not charge and I'm reading 12 volts with the engine off and 4 volts upon starting the truck. I have replaced the alternator tried 2 voltage regulators and have rewired what was already badly wired. When I jump start the truck it runs the battery down and when I jump the field wire I read 17.8 volts at the battery. I thought at first it was a bad regulator, but now I'm wondering if it's a bad cell in the battery.

When the truck is running would the alternator still put out 14.5 or so volts if the battery is bad or would it just not even bother to try and charge it? Also what is the exciter for the alternator?

On my regulator I have the F terminal hooked to the field on the alternator and the A hooked to the fusible link wire on the alternator the other two terminals are not wired to anything. I have an actual gauge not an idiot light, so the I'm guessing that's why the I terminal is open and the S terminal was hooked up to the horn relay, but since I don't have a horn in this truck I unplugged it.

Let me know if I'm missing some info. As of right now I can only figure that the battery is bad or I'm missing some sot of exciter for the alternator. The trucks wiring is far from stock, so color coded wires are none existent.

Thanks guys.

[fordman]

here are the 71 wirign diagrams. http://www.fordification.com/tech/wirin ... _quick.jpg sounds lik ea bad battery to me. but i am not sure i am following what you are testign or how your testing it. other may chime in who know more than me.

[Skitzo]

Thanks, I checked out that diagram (as well as the others) and it doesn''t tell me much as far as where those wires are hooked up. For instance the Green-Red wire, what terminal on the regulator is that hooked to and what's it connected to on the other end? On another note, I have a good ground to both the alternator and the regulator.

[Thunderfoot]

You have to have an "Exciter" wire to the Voltage Regulator or the alternator will never charge. The Exciter wire is what tells the charging system to turn ON. This wire is a resistive wire from the ignition switch and normally is either a Black wire or a Purple wire and then turns to a Green/Red stripped wire in the engine compartment, it is sometimes routed with the Horn wire by the Voltage regulator so that may be were yours got tossed... If you have to run a new wire from the ignition switch you will need to add a about a 560 ohm resistor in the line. (The black or purple wire section is the resistive part of the wire in the stock wire harness in the truck)

[Skitzo]

Awesome, that is good news to hear Thunder. I knew something was rotten in Denmark when I saw the poor wiring job done by the previous owner. I'll see if I can't hunt down that Green/Red stripped wire. One last question though, does said exciter wire hook to the "A" terminal or the "I" on the regulator?

[Thunderfoot]

It depends on how your truck was wired at the factory, seems to be somewhat dependent on if your truck had full gauges (alt gauge) or idiot lights (alt light). I'm guessing that beings you only have 2 now that yours was a 3 wire setup but here is the info for both.

The 3 wire setup uses terminals (F,S, and A) they don’t have anything wired to (I) and the Exciter wire is connected to the “S” terminal and there is no stator wire connected to the alternator. so ;
F terminal on the regulator connects to the field connection on the alt.
S terminal on the regulator connects to the ignition switch. (turns regulator off & on)
A terminal on the regulator connects to the battery +( Plus) or positive terminal. (senses voltage of battery)
I terminal on the regulator not used.

For the 4 wire one.
F terminal on the regulator connects to the field connection on the alt.
S terminal on the regulator connects to the stator connection on alt.
A terminal on the regulator connects to the battery +( Plus) or positive terminal. (senses voltage of battery)
I terminal on the regulator connects to the ignition switch. (turns regulator off & on)

[Skitzo]

Yep I have a three wire, I also goofed I should have asked either the "S" terminal or "I" terminal not "A". My buddy just brought his 71 over to my shop so I could look at his wiring and indeed I am missing the Exciter wire. The whole connector in fact and it looks like it was fried all the way into the cab, Hence no horn and no exciter. This site is the best, thank so much for your help!

[cookmatt67]

good info

[Jaustin]

What's the resistor wire for and what would happen if you didn't have any resistance?

[GHOST]

great info..I was having the same problem with my sons truck [ GHOST II ]...I love this site...