LS3 Alternator One Wire **SOLVED MY PROBLEM**

1986 Porsche 944 Turbo with LS3 crate motor 480hp.

Problem:  
Alternator stopped working after bouncing from 10v to 14v over a couple of days.  It died after 1000 miles of use.   PISSED!!!   The alternator is mounted on the low driver’s side with 3 bolts.  The single orange exciter wire plugs into it from the LS3 engine computer.  I later learned this alternator is normally used in a 2007 CTS-V Cadillac LS2 6.0 engine.  This was sent to me from RH as new and I was told it was a 105 amp alternator.  

What I learned after networking with my local quality alternator rebuilding shop:
1. He looked at it and said it was a 180-amp alternator rebuilt with electronics from one of three other countries that sell cheap electronics for rebuilds.  He asked me to find out how many volts my exciter wire was putting out.  If it was 12 volts, it was too much and need a resister to bring it down to around 5-6 volts.  Unfortunately, I could not test this until I put the alternator back in.

2. I looked all over the internet to find out what voltage this engine computer put at the exciter wire and no luck.  I then took the shop advice and went with turning this into a 1-wire alternator.  Literally, only the 6-gauge charging wire is connected. It turns on by sensing when the pulley wheel is turning.  I attached a paper showing all the specs which I found very helpful.  There is no exciter wire and no need to rely on the “optional” alternator wire from the LS3 computer.
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NOTE:  From the paper showing alternator RPM which is about 1/3 of engine RPM, the alternator is turning on at about 1/2 of engine idle with a 2 second delay.  This allows you to start with out the alternator active and not have to rev the engine to get it going.  I love it.  Works great.

Solution:

I now have an OEM ACDELCO alternator rebuilt with quality parts that is all regulated with one wire connected to the battery.  All the rest of the work is inside with the regulator, rectifier, etc.  It has the capacity for 180 amps but I am sure it will never need to go that high.  I have a 150 amp circuit breaker.  I know, I know…….that is less than the possible 180 amps that the alternator can put out.  So far I have never popped the breaker so until then I will save my money on a larger circuit breaker for later.

This write up was intended to promote the one wire alternator so that you don’t have to pull your hair out trying to get it all wired up or if your wires are all garbage, you won’t need them now.  


Elephant in the Room:

What about the blue wire going to your Porsche 944 dash light.  I don’t use it.  I simply don’t have this light working in the dash anymore.  I am fine with just seeing my voltage gauge go up to about 14.2 volts when the car is running and it makes me very happy.  It is the only dash light that is now inoperable.  NOTE:  On the way out the door of the shop, I asked him if the new electronics were made in the USA since the new sticker shows MADE IN THE USA.  He said no, but that they were very high quality parts.  I assume they have figured out where to buy them instead of China or the like.

the one downside to a one wire alternator is they dont always excite at idle, sometimes you need to give the engine a little rev to get them to excite and start charging. i tend to be a little more mindful of the charging voltage on cars with a one wire alternator as ive had it where i fire a car and im doing other things (filling transmission, topping up coolant, etc), the car warms up and the fan comes on and kills the engine and now the battery is dead. if your paying attention to your gauges it shouldnt be an issue though.

for the record, the charge light on the 944 is where the power comes from to excite the alternator. the bulb essentially acts as a resistor dropping the voltage. if the alternator was to have a fault the regulator grounds the circuit and then the light turns on. many automakers have used this method over the years. for what its worth, ive been running my gm cs130d style alternator on my 944 issue free.

in the 2000s gm started controlling alternators with the ecm, some of them just used a voltage signal to the same alternator as would use a bulb and turn the alternator on and off as it wanted, while others used a much more sophisticated circuit to control the actual charge current. the ls3 for sure would have used this, while the ls2 may be either or.trying to run an ecm controlled alternator off a light bulb will work for a while, but usually not for long.

Just buy a heavy-duty Bosch or similar name-brand with lifetime warranty.

P.S. what transaxle are you running to hold that 480hp ?

MotoRider42HC wrote:Just buy a heavy-duty Bosch or similar name-brand with lifetime warranty.

P.S.  what transaxle are you running to hold that 480hp ?

1. Reference your lifetime warranty. I read write ups from the corvette groups and many other LS conversion groups learning that the lifetime warranty continues to replace the bad alternators with cheap China, Mexico and Malaysia electronic regulators and electronic parts which fail. You may have a lifetime warranty, but you will be replacing it often according to the majority of posts I have read. Sometimes you get a good one, but the odds are very low.

2. Reference the transaxle. I have the original stock 944 Turbo transaxle. I only put locking bolts on both ends of the CV joints. Works great.

very true, Chinese $#** is Chinese $#**.

I had issues as well at the final stages of my swap.  



I sent my alternator to a semi local guy to have it checked out decided to go ahead and have it converted to a one wire while it was there. Now it is just one of those things I check along with oil pressure after starting the car to make sure it's charging correctly. Been very happy with it so far.

Lots of good information in this thread, thanks to you guys for taking the time to share it.