we swapped a 95 lt1/t56/stock pcm into a third gen, i think its a 90, anyways everythings is in and fired up however the alternator isnt charging, the battery keeps dieing, we tried three different alternators, same result, not charging.

is there something were missing????

 

https://www.thirdgen.org/techbb2/sho...LT1+Alternator

There is a wire in the C220 (if I remember correctly) That has to go to a 12v source with a 470ohm 1 watt resistor. The above thread will explain.

 

sweet thanks!!!!

 

Same problem I had. You wouldn't think just a little 10 cent resistor would make a difference, but I does.

 

Ah, that might explain what happened to my LT1 alternator...I thought that wire just went to battery voltage with no resistor, and when I fired up the engine for the first time, the alternator started pumping out full current, and brought the electrical system up to 20 volts. Fortunately the only thing it killed, apart from itself, was a headlight and most of my battery's remaining service life, and I had a spare alt lying around from the 2.8L I pulled, which went on with only a little modification. At the time I thought it was just because the LT1 alt was from a flood car...

 

Does this apply for the LS1 as well? I just had it installed into my '83 and I only have 2 wires on my alternator. One really thick wire going to the + post on the battery and one small grey wire going somehwhere else. I am on my forth alternator so it sounds like exacty the problem everyone else has had.

 

I tried the resistor thing on my LT1 and it didn't work. What I ended up doing was just put the 12v wire without the resistor on the F terminal, and now it works fine.

 

Sorry, but what is the F terminal?

 

On the connector for the alternator there's some letters for each wire. One is "L" for light, one is "F" for field, "S" and "P". There is no wire at the "P" terminal and the "S" terminal would go to the battery as it would be an output from the alternator. I just hooked a wire to the bolt stud to the battery instead. Here is a picture for you.

 

Ahh, I will have to get under there to look. I only see one skinny wire attacked and I can't see the connecter. Thanks!

 

Mine was the same way, one single skiny wire going to the alternator connector. I tried the resistor thing and blew two alternator so I posted on here and someone responded with this.

"This is a common problem that I luckly avoided.
Here is what I found that helped me save my alt.
I have had my alt. hooked up this way since completing my LT1 swap with no problems and I am using a 95 F-body alt.
Basicly just disconect the wire you are curently using on the L terminal and conect IGN +12 VDC to the F terminal
Here is the link I found the info on
The L and F pins are on the conector that plugs into the alt and they where labled on mine.

http://home.sprintmail.com/~halmc/veeeight.html

Another prob. that I have encountered is that the alt. A Camaro has two wires, One heavy one that is mounted with a ring terminal to a stud. The other is attatched to the "L" terminal. The heavy wire goes directly to Batt. positive. The other has a 470 ohm resistor in it and this goes to IGN on. I have blown two alt's ($190 a piece!). I decied a little more research was needed . I discovered that the resistance needed is dependant on what else is in the circit. The final voltage is VERY critical. The solution is to forget about "L" and the resistor altogether. Instead, feed full batt. power (from IGN) to the "F" terminal (Field). I have recommended several people use this method on differing applications and so far, not a single failure"

the link doesnt work anymore but you just need to go down to advance auto or autozone and pick up a GM alternator pigtail. if the guy looks at you like you have two heads tell him you sure he has it! then just do like the instructions say. this works like a charm, and you dont have to worry about resistors or crap like that. ill try to get a pic of my connector. hope that helps

 

I can honestly say that something was probably wrong with the resistor (or the alternators) then, there are several people that are running the resistor inline, plus this resistor is embedded in the 4th gen dash, inline with the volt meter in the dash. You have to have a 1w resistor, anything lower than that and it will overfeed the alternator and blow it. I showed what I needed to my father-in-law who has been doing electronics for 40+ years and that is what he advised me of when he saw the diagrams that I showed him.

I've been running the resistor, inline off of the C220 connector on the LT1 harness for over a year and still have the same alternator, it puts out 14.1 volts at the battery. Plus I have mine hooked to a switched 12v instead of a constant which is what the older style alt. have, is 12v constant to the alternator. The 4th gens are on a switched source.

 

Ya thats pretty much what everyone else said and it didnt work for me. I was overcharging like a mother, blew all my head lights. I did get the resistor option to work ONCE and that was only for an hour, then all of a sudden the voltage spiked and killed the alternator AGAIN. so by just switching the feeds on the alternator you dont have to bother with the resistor, just feed it 12V and its happy Ive had it wired this way for about 3 years and I know a bunch of guys in the Jeep forums do the same thing and dont have any problems. IMO its just an easier way

 

So basically you are saying take the wire from the L terminal and hook it to the F terminal? Currently the L wire is hooked up to the PCM according to the shop that did the work.

 

I dont remeber but with out the resitor is the L a 12V hot line when the ingnition is turned on? if it is the just cut it and run it to the F teminal on the new plug.

 

The wire going to the L terminal has to be hooked to a switched 12v source, that's what keeps the power feeding into the regulator all the time. If it's hooked to the F it should be hot all the time like the old 2 terminal alternators are.

 

Exactly, and you no longer need a resistor. just find a hot 12V acc line and hook it up. I was pulling my hair out for 2 weeks trying to figure this out and when I was shown this I couldnt believe it was that easy.

 

I dunno, I didn't want to re-pin anything if I ever decided to buy a 4th gen body and put the LT1 in it later. I have every plug in the LT1 harness untouched so all I would need to do is pull the motor, and put it in a 4th gen. I just spliced the alt wire into the old cruise control wire under the dash, it turns on and off with the key.

 

Hot all the time when the key is in the on poisition? Or just hot all them time period?

 

only when the key is on. and as far as haveing problems swaping into a 4th gen later. It would be just as easy as having a resistor. the only thing your doing on the tirdgen is finding or running a seperate wire that is hot when the key is on. you wouldnt even need to cut your existing teminal off you could just tuck it away. so by switching from L to F you dont NEED to cut anything on you wiring harness. you just need a key on 12v line

 

That is exactly what I did with my alternator.

 

The original alternators had 12v hot all the time, the LT1 alternators have hot with key on. If it was hooked to hot all the time, it would keep the regulator hot all the time burning it up.

 

Mine is wired so that it only receives 12v when the key is ON. I just used the wire that would have the resistor in it that goes to the "L" terminal and took out the resistor and wired it to the "F" terminal.

 

If your field terminal is 12v constant not switch it will drain your battery. maybe not overnight. What the field terminal does is turn on the magnetic field in the alternator. The weaker the the field voltage the higher the alts output . Basicly your "F" wire needs to be a 12v switching that is not connected to anything else. Otherwise it may sense low voltage and increase the output.

 

Is there a way to tell if the alternator is "excited" all the time? I checked the voltage on my car while it was running and it was holding steady at 12-14v. I'm not sure I want to mess with anything if it ain't broke. but on the other hand it has fried 3 alternaters before this (I made it 10miles on the second one, third one died in shop, 4th one got me home over an hour away, and I've only started it to work on it since)

 

I'm trying to get my alternator working, it may already be fried. I'll be getting it tested tomorrow and picking up a new one, if necessary.
I stopped at Autozone and picked up a new pigtail, located in the aisle with fuses, at least at the local store, not behind the counter. There were no instructions with the pigtail as mentioned above.

So, I'll be giving this a try.
"L" not used
"F" wire to 12v switched power source
"S" wire to stud on back of alternator
Stud to postive battery terminal

thanks
don