Recently installed a new wiring harness in my 75 f250 - external regulator - it seemed that there was no wire from the ignition switch to the regulator so the alternator was not charging the battery. I installed a wire that extended from the ignition switch prong that was hot when the key is in the on position and wired it directly to the "S" prong on the voltage regulator.

I just noticed today that there were 3-4 melted spots in the wire. I have no inline fuse installed in this wire. Would the melted spots be the result of too small of a wire? I believe it was a 16 gauge wire that I used. When I connected it to the ignition switch, I actually used a splice like this:


When I pulled the splice apart, the wiire that I installed had a melted tip where it went to the splice. The wire also was melted to itself in another place where it looped around under the dash. Another point where it metled was very close to the plug at the regulator. There are two wires that come out of the "S" terminal of the regulator. One goes to the ignition switch and the other one goes to the alternator. Those two wires were melted together near the plug.


What did I do wrong that caused this melting to occur??

I need to replace the wire and would like to be sure I get it right so I don't have the same problem.

Thanks.

 

Why did you hook a "s" wire to the alternator? That's not correct. Here's the correct way;



There is no connection to the "s" terminal if you do not have a electric choke. There is also no connection to the "I" terminal of the regulator.

There is another way to wire it using the "s" terminal of the reg to the alternator, and it also uses the "I" terminal. But you have to wire it one way or the other, not some combination of the two.

 

Ok. So, here is what the Painless harness instructions show.



I do have the Ammeter as shown above - not a charge light.
I do have an electric choke - (Edelbrock 1411 carb)

The green/red wire actually shows that it leads to the charge light (which I do not have). Since I do not have a charge light, should I remove/disconnect the wire that leads from the "I" terminal of the regulator?

The diagram below also shows the wire going from the "S" terminal of the regulator to the "STA" on the alternator. You mentioned that this should not be there. I do have an electric choke - which is wired to the fuse box and is only hot when the ignition switch is on. Again, this was how the harness was wired.

I would not have any problem changing the wiring around to match the diagram you posted above - I just want to be sure that it will work with the set up I have.

Always appreciate your help.

 

Don't worry about the choke, yours is aftermarket, leave it wired to the key-on power like you have it.

The painless wiring is the other way to wire it. Either follow their diagram, or follow mine in my previous post. You put a key-on hot wire to the "s" terminal of the regulator. Why did you do this? That's your problem.

Either follow the painless wiring diagram you posted, or wire it like the one I posted. It's your choice, it will work either way, but don't add or leave anything out of either one.

 

I am a bit confused...sorry for making this difficult.

If I remove the wire that I connected to the ign switch (key on hot) and the "S" terminal of the regulator, the alternator does not charge the battery. This is how it was before I added that wire. But, you are saying that this is where the problem is. So, if I disconnect that wire, what do I do so the alternator is charging the battery?

This is the thread that I had started when I was having the problem with the alternator not charging and why I connected the wire from the ign switch to the regulator.
https://www.ford-trucks.com/forums/1...ats-wrong.html

 

There are two ways to apply power to the voltage regulator, so that it will bring the alternator online:

(1) Apply keyed power directly to the S terminal. This closes the field relay in the regulator, which in turn applies power to the field terminal of the alternator anytime the key is on. When the alternator turns with power applied to the field terminal, it produces current. In this configuration, there is NO connection between the regulator S terminal and the alternator S terminal. The I terminal of the regulator is unconnected. This is consistent with the diagram Franklin2 posted.

(2) Apply keyed power to the I terminal through a charge light. This applies a pilot voltage to the field terminal of the alternator, so that it can produce current once it turns. Once the alternator produces current, voltage at the S terminal of the alternator (which is connected to the S terminal of the regulator in this configuration ONLY) closes the field relay. This is consistent with the Painless diagram - except they do not show that power is coming from the other side of the charge light.

You have to do either or. You can NOT do both. If you wire it as shown in the Painless diagram, you can NOT apply keyed power to the S terminal of the regulator. As Franklin2 said, wire it one way or the other. Do not add the extra wire (you already found out why).

 

I think this is all making sense now.