.boB

Yes, I know. Another alternator question. There are dozens of threads and questions about this, and seemingly endless answers. This appears to be much more complicated issue than you might think. I have spent hours reading through a variety of threads, on a number of message boards.

I'm installing a stock LS1 into an Exocet track car. The drive train came out of a 2001 Firebird. I have a Megasquirt ECU to run the engine; and a Painless Wiring basic chassis harness for everything else. I do not want to run the alternator through ECU for a variety of reasons. So I'm using Alternator Exciter wire from the chassis harness - white #914.

As I read in a lot of places, I placed a 470 ohm, 1/2 watt resistor in the exciter wire, which cuts the power down to 8.56 volts (engine off). Unfortunately, the brand new alternator will not charge.

So then I started perusing the Painless Wiring tech section. And I came across something not mentioned anywhere else.



This shows two wires for this alternator - one with the resistor, and one with 12v. Painless also sells an adaptor kit, with the right plug and a 85 ohm 5 watt resistor in it (which can certainly be purchased cheaper), designed to adapt the new alternator to older cars.



So, has anyone used this method? Am I on the right track? Since no one else has mentioned this, am I way off track?

charchri4

My alternator is from an 02 F body and I didn't put any resistor in the wire. As I recall there is only one wire in that 4 wire plug and it's keyed hot. But I am using the wiring from the Camaro so perhaps there is something in the harness? I know it's not at the plug because I accidentally chopped it off and replaced about a foot of the wire leading up to it. Don't know if it's right or wrong but I'm pretty sure I'm feeding mine 12v.

Full disclosure I did toast an alternator but that was shortly after I put a hole in the hood right above it and washed the car. Voltage went to 18 and after a key cycle it would no longer charge. After the new lifetime napa unit went in and the shield went over to keep the water out it's been fine so probably not the wiring.

.boB

If you're using the harness and ECU from the F-body, then the alternator is controlled by the ECU, and receives a 1-5v signal for control. Then it's easy, because it's plug and play.

I'm going to pick up a 2 wire plug and a new resistor and see what happens. I'll let ya know how it works out.

.boB

OK, it's fixed. This is the Real Answer.

The F-body LS1 uses a single wire alternator. This single wire is connected to the ECU, which controls the charging rate. The charging rate is controlled by a program that varies the charge depending on things like temperature, engine load, throttle position, etc. Mostly an attempt to gain more fuel mileage.

If you install the LS1 along with the stock ECU and wiring harness, just plug everything in and don't sweat it.

But if you're using an aftermarket ECU or a carb, then you'll need to use a 2 wire plug, a resistor, and a diagram similar to the one above. There are a couple of differant ways to accomplish this goal, but this is the one I found easiest to do. I connected this up this afternoon, and immediately got 14.10v.

Unfortunately, I did not find this information in the instruction book for the Painless Wiring harness.

In previous reading, I found many people who stated to simply place a 470K ohm 1/2 watt resistor in the line, and it would work. But, that didn't work for me; I don't know why.

I am using a Megasquirt MS3+ ECU. I could connect that one wire into the ECU, and it would control it in the same way the stock ECU does. But I was concerned that if the alternator started to fail and got noisy, it could take out the ECU. Maybe that can't happen, and I was worried about nothing. But keeping them separate like that helps me sleep at night.

acedeuce802

I'm just looking for some clarification on this. I'll be using Megasquirt as well. I picked up this alternator (LS1 Chevy Camaro Firebird Alternator 2002 01 00 90 1998 Generator | eBay) which is a 98-02 F-body alternator. I have also always heard that these are a 1 wire alternator. Even when the ECU isn't in the mix, because 98 Camaro's just use 1 wire to a light on the dash. Any idea why these require 2 wires in this case?

.boB

In stock form, it's a one wire control. That one wire comes from the ECU. The ECU uses a fairly complicated control algorithm to improve fuel mileage.

The MS3+ is capable of performing the same task, just like the stock ECU. I don't really need all that, since it's a track car. But you could do it, and then still keep it as a 1 wire control.

BTW, if I was going to do this again, I would get this: http://www.efisource.com/shop/ms3-lsx-plug-and-play/