This subject is covered at length on the HAMB. There is one problem with using a 3-wire and an idiot light...this setup can and often does backfeed through your ignition system causing your engine not to shut off. The standard wiring diagram has the #1 wire leading to a dummy light, then to the ignition switch. The #2 wire jumps to a non specified positive. When this system works, it works flawlessly. However, the system can backfeed and overload the ignition switch. Since there is no regulator, there is no stop gap between the alternator and your ignition which is a huge no no. Speedway sells a diode you can install that acts as a stop gap between the alt and ignition switch, thus eliminating that problem. If you intend to use the idiot light option, it is a must have item. Sorry if this has been covered already, I skipped a few posts. Other than that, the 12SI is a stout alternator that can take a beating.

I am running a GM 3-wire 100A on my 289 that I got from Advance Auto. (SHHHH....don't tell anyone) In the box from the re-manufacturer it shows the multiple wiring diagrams. One of them is jumping the #1 terminal right to the + on the alternator, which is a direct feed to/from the battery. There is nothing questionable there as long as you use good wire. This wire can be a 10 or 12ga wire for the jump. The wire off of the alt to the battery NEEDS to be decent sized or you are essentially bottle necking the power feed...thus causing your lights to dim. I have a 2ga wire feeding from the alt to the batt side of the starter solenoid, and 2ga wire from there to the battery. I ran this setup all year last year with plenty of power to spare. My lights never dim. The only thing I needed to do was cut down a piece of aluminum tube for a spacer and use the stock Ford brackets. If my tube was slightly smaller in diameter and had a cleaner cut, it would look stock. I have a light installed in my dash that is not hooked up at this time because I cheaped out and have not got the diode yet.

 

^Wow, I have yet to have been told this...Interesting.

So where exactly in the wiring is the diode placed? Can I get this diode somewhere locally?

I was told 10ga wire from the alt to the solenoid, is that not enough?

 

Boy, I sure can't see how you could backfeed, unless you set up the alternator output to go to the load side of the ignition switch?? Can you point out the backfeed path?

Morot has what appears to me to be an older ~40-60 amp GM alternator; for that I told him the 10 gauge would be adequate. It would not be for a more modern 100 amp unit. It will only put out what is needed anyway, and it is not likely to "peg out" with his minimal accessories. Comments?

Morot, why don't you just jump the terminals for now to get it up and running, and screw around with the light later?

 

To the best of my knowledge....so this can all be disprooven...the light works like this. The #1 wire is a wire that is hooked to the stator (there is your direct connection). When the stator is activated, this wire becomes either a field, or a light power (I cant remember which). When the stator is not activated, this becomes a ground, thus completing the circuit and turning the light on. The main power source for the dummy light is your ignition switch. If what was told to me is correct, this is when it gets fun...the alternator is on constantly because you switch off of the battery power, so basically from 1 RPM, your stator is generating power. When you shut your car/truck off, your stator has an electrical current built up that needs released. Often it simply flows to the battery, but it can just as easily follow wire #1 to the ignition switch (backfeed) and cause your ride not to shut off. The diode prevents this problem....IF you are running the light.

If not, you can let wire #1 be, jump #2 to the battery post (on the alternator) and it works great...just with no light. I personally intend to purchase the diode this year cause I have no ammeter or volt gauge off the alternator. I would like to know if it is working or not. I would also like a working gas gauge...but that is still to much to ask for!

Also, an alternator puts out what it can...not always just what is needed. It does not care if you only need a little...it puts out what it can which is somewhere around 70% of the rated power. For example mine is supposed to be a 100A alternator that probably puts out around 70A. Battery cable and alternator cables are (insert personal prefrence here) items that I feel the bigger is better motto fits well. I would say 2ga - 4ga wire...no smaller. Most cars come factory with 4ga battery cables to give you an idea. The jump wire...eh...I just used what I had laying in the garage, which happened to be a 10ga, which works fine.

 

Would posting a picture of the unit help you determine exactly what amperage it is?

My issue with actually doing the swap is that my truck is currently my DD and don't really have another vehicle ready to replace it. The generator is doing the job for now.




This whole topic on exactly how the BATT light works has come up and been argued multiple times.....I'm not really sure what to believe!

 

You can believe this, if it was a non issue, Speedway wouldn't waste the money to make something to prevent problems. Running the light without the diode will cause issues. Not using the light...it takes all of 20 minutes to install the alternator. It is honestly as simple as hooking the power cable and jumping the terminal to the battery cable. The only hard part is adapting your current setup to mount it.

No...posting a picture of it won't likely tell anyone how much it pushes out.

 

Funny that MAD electric should be mentioned. I spent about 2 hours on the phone with him after reading about his stuff on a different website and forum.

I ended up buying his re-wire kit and it came with 2 of those junction blocks. I plan to use one to relocate my battery to the bed of my truck and power the air pod from Ride Tech off it and the other under the hood for the lights and possibly an electric fan.

He is also a big fan of the 12si alternator. I plan to get one.

 

OK, so I get it. FOR NOW, I can basically hook up my Alt system and as long as I leave the BATT light unhooked, I won't have to worry about the theoretical "backfeed". Correct?

My issue? I won't know if the dang thing is working and if it somehow isn't, I might leave myself stranded with a dead(brand new) battery.

 

I am not meaning to come across as harsh, I am sorry if I have. You can hook it up however you want...I am not trying to be rude. I am just trying to explain things to prevent a probable issue. The diode is only like 8-12 bucks from Speedway...if you want your light to work then get the diode. It is an inline install, barely takes a few minutes to splice it in, and they ship things fast.

Outside of that, after you install your alternator you can take it to any box parts store and have em test your charging system, you could have your alternator bench tested before you install it to make sure it is working...there are ways to make sure things work. Honestly though, the wiring side of it is easy and fool proof. I am a wiring dunce...and if I can do it and understand it...I believe anyone can. If I get a chance this weekend I will snap a few pictures of my alternator setup on my 289 so you can see it if it helps.

The last part of my spring fixin plans will be to install an inline diode and get my alternator light working...cause I too would like to know. The other thing you could do would be to install a gauge, but by the time most people notice a dip in the volts, the damage to the battery has been done. Here is the Radio Shack #....#1N4001 Here is the Speedway # Part #910-64100. The other side of the light should be on the ACC side of your ignition switch.

 

Remember, the whole point of converting to an alternator is that they easily go 100,000 miles without any problems. Having a light is nice, but mostly for people who come to an alternator from a generator, who are conditioned to expect problems.

A different way to monitor it is to get a "gauge" at AutoZone or wherever, that plugs into the cigar lighter and has red, yellow, and green LEDs, to indicate voltage level.

 

About this diode, do I need like a certain level or amperage? How do I know if it's enough to handle the job?


Ross--Your saying the generators are known for issues? Why?

P.S. can you also look at https://www.ford-trucks.com/forums/1...l#post10038871 I don't understand how I am supposed to splice such a fuse into a wire....seems rigged.

Thanks a lot guys.

 

I think you are over-thinking this. You could add the fuse and the diodes at your leisure down the road.

If you look at Julie's old schematic that I marked up, where I showed the fuse or a fusible link, that was for a truck with an ammeter, where the lead from the BAT went all the way under the dashboard, thru the ammeter loop. I "recommended" the fuse in that context because there's a good amount of potential for that wire to short somewhere under the dash, before the fusebox. For your setup that isn't a concern. So fuggedaboutit...

Generators themselves aren't so troublesome, it's the regulators. There is always something not exactly right with them. But generators do wear out brushes, have field shorts, etc. so they aren't flawless either.

Diode: any diode rated for 25 volts DC, rated ~5 Watts or so will work. But it matters which way you put it in. Maybe you should just buy the one 49 linked to.

 

Stick a volt-meter in your truck!

Anything less than about 13v means it's not charging.



Um, Diodes are not rated in WATTS. ..............They're rated: peak inverse voltage (PIV) and current handling in AMPS or milli-amps.

A 1N4001 is rated at 50 PIV (Vrrm) and 1A. It only has to pass the light bulb current..........and It's only there to prevent current from flowing the other way.


Cheers,


Rick