I have a 03 7.3 diesel f-250 with single alt right now. I would like to upgrade to a dual alt setup. I have done alot of reading on this today and have a couple of questions with the wiring. Would i be able to run a wire from the first alt to the second to turn it on and off(the control or exciter wire whatever it is called)? Can i run the second alt off of a keyed ignition wire? Is there going to be any problem with my pcm or throw any codes. Any problems with overcharging. Thanks for any help you can send this way. I have two big amps for the stereo and am installing a full computer and have a bunch of other electronics that need power so i would rather have two alts than one big one for reliability issues. Thanks again

 

I think the stronger of the two amps would become the main, and if the battery/12v system didn't need anymore power the second alt would reduce the output. You can turn the field on/off with a 12v signal. Without the field, an alt puts out very little voltage. I am sure someone will have more info.

 

If you can find the schematic for an Ford F550 ambulance all the info is in that.

 

I think your situation may be better served by adding a third battery with an isolator. Have you considered this?

Even with two alternators, they are not going to be able to react to the sudden music surges from a large stereo, were a battery will. You could mount the third battery close to the amps, and you would not need stiffening capacitors at all. When a big music surge hit, the battery would be there with all the reserve they would need, especially at idle when the the alternators are restricted because of rpm. You could also play the stereo and computer with the truck off, with no danger in running down the starting batteries, so that would cover your reliability concerns.

 

A third battery would be able to keep up but only for a little while. Trying to charge three batteries off one alt( i believe 110 amps) is just going to put more strain on the alt which is what i was trying to avoid. Two 110 or 140 amp alts would be able to keep up with everything alot better than one 110 amp alt. I used to compete in car stereos and batteries drain within minutes and need to be recharged, where two alts come in to play. If anyone know more about the wiring or has an ambulance package schematic like mil1ion said it would be extremely helpful. Or know how the pcm will react to two alts? Thanks for your help

 

I looked at a 2003 van with dual alternator schematic.

The two B+ output wires are tied together.

The two "A" terminal wires are tied together.

The rub comes in with the "I" terminal. Each "I" terminal has it's own spot were it goes back to the PCM. I am not sure what role the PCM plays in this whole thing. The "I" terminal turns the alternator on and off. You might want to call the local Ford dealer and see if a PCM with dual alternators is different from a single alt setup.

P.S. The superduty truck in 2003 had a dual alternator option too.

 

From what i read the pcm is different and it does have a wire going to each alt. It runs the primary alt until voltage drops and then turns the secondary on to generate the extra power to bring the voltage up. I read on a gm forum i came across while searching that some company came up with a kit to upgrade from single to dual alts and they just used a ignition on wire so the second alt was running all the time and it was voltage regulated so it didn't send to many volts to the pcm. It also said that the gm factory dual setup had two wires going to the pcm. I believe this is the only difference in the pcm and from the reading i have done they found it better to have both alts run all the time cause it lessons the load on the primary on and they should last longer, two alts working half as hard as one alt working overtime and heating up. I found a really good price on the bracket, what looks like a factory wire harness that plugs into both alts and goes to the battery, second alt, pulleys, and tensioner. So all i would need is a belt and the bolts to make this work. Thanks for all your help, I believe i am getting alot closer.

 

I talked to Jody Tipton who owns Dp Tuner and he said that the pcms are the same for the dual and single alts. Franklin2 said that each alt had a seperate "I" wire rinning to the pcm. I found a ford wire harness for the dual alts but it doesn't go to the pcm(from what i read), it runs to the battery and between the two alts with plugs on both ends. Thanks for sharing any knowledge on this.

 

I am thinking the seperate PCM wires are like you said, to have some sort of fancy control over the alternators.

In the old days, even with engine computers, all they did was go from the ignition switch "run" 12 volt power, to a "gen" light in the dash(with a plastic socket and two wires), came out of the other side of the bulb and went out to the "i" terminal. When the key was turned on, the "i" terminal was low, and the light came on in the dash. Once the engine was started, the "i" terminal went high, and the light went out.

So I think your options may be to hook both "i" terminals together, or you could wire a manual switch to the "i" terminal and mount it under the dash and turn the extra alt on and off. I would hook the other side of the manual switch to a hot in run and not the battery, in case you forgot to turn it off. If the "i" stays hot with the engine off, the battery will drain down.

 

After alot of research i finally got it all figured out. thanks for all your help. With alot of help from Ed at y2kfordparts.com we came up with all the part numbers and everything i would need. It comes to less than what a high output alt would cost and i don't have to worry about an ho alt that is wound tight which decreases the life of them since they are working alot harder. The ford wire harness that goes between the two alts and just plugs in ties everything together. The pcm doesn't matter if you have 1 or 2 alts. I ordered everything yesterday and hopfully will get it the begining of next week. If anyone is interested and needs some help gathering parts let me know or talk to ed who will be able to get you everything you need. Thanks again for all your help.