Ok, so I know that with the LS1 alternator you need to wire a 500 ohm resistor between the alternator pigtail and the brown wire on the stock harness. My question is what do I do with the other end of the brown wire? The brown wire goes through the bulkhead connector and used to go to the choke light on the dash. I'll be using a full Autometer gauge panel, so can I just connect the other end of the brown wire to the back of the Autometer volt gauge? Basically will it work if I wire everything together like this?

Alternator --> resistor --> stock brown wire --> Autometer volt gauge

 

Wait...why do you need to wire in the resistor? You're using 100% aftermarket gauges right? What motor/pcm are you using?

J.

 

i think you should be ok cause im using my factory gauges and did not use a resistor. Im pretty sure those aftermarket ones are plug and play

 

No resistor here either. Brown wire straight to stock volt meter 3yrs no problems

 

I remember having to use a resistor on my LT1 swap, but not my LS1 swap

all my guages work fine in both cars

-jason

 

I could've swore I read somewhere on here or LS1tech that a 500 ohm, 1/2 watt resistor should be wired between the alternator and the brown wire, then the brown wire should go to a keyed ignition source. The reasoning behind the resistor is to reduce the voltage from 12v to 5v which is what the PCM does to tell the alternator to charge. I'm using 100% Autometer gauges and I'm not using a PCM because I'm going carbureted, which is where the confusion comes from. Basically I just need to know 1.) should I use the resistor? 2.) where should I hook the brown wire up to: the back of the Autometer volt gauge or a keyed power source in the fuse box? Isn't the volt gauge a keyed power source?

 

Odd

The Alt has a single wire on Fbody LS1's which is controlled 100% by the PCM. What alt are you using?

 

the resistor is for the tach signal wire, to bring the voltage up from 5v to 12v so the stock tach works

-jason

 

Um....no.

 

I'm using a stock LS1 alternator. The pigtail has one red wire coming out of it.

 

Ummm Yes, I am running it that way now, as described in this post

http://www.ls1tech.com/forums/conver...l-no-tach.html

http://www.ls1tech.com/forums/conver...-tach-yes.html

thanks for playing!

-jason

 

Ohhhhhhhhh... NO PCM. There is the key

Im still a little confused about your question though.

The LS1 uses two wires. One is the big one on the back, and the other is a tiny wire in a plug...the exciter wire. Its basically a field trigger wire. It recieves a 5v signal from the PCM when its supposed to charge. Thats why they made that wire so unreasonably tiny. Because it only sees 5v. (re-read the thread...you already know all of this. But I typed it, so Ill leave it haha)

So....if you arent using the PCM, you will need to find a way to reduce the 12v to 5v that the alternator wants to see to know to charge. The only thing Im not sure of, is if you can just do that and not have the alternator overcharge the battery. But Ive read plenty about guys running a 500 Ohm resistor on that and just hooking it straight up. But Im not 100% on that resistor, because Ive seen a few different values for that.

You wont be running that red wire to the back of a voltage gauge though. The voltage gauge just shows you the voltage of your system. So you want to hook that up to a GOOD 12v souce. The best point of connection would be the positive battery post. You dont want to piggy back that onto a smaller interior wire for example.

Another solution is to find a good old GM 1-wire that will fit. Ive heard of guys finding them and ordering them from summit. These work off of engine RPM, and will eliminate the need for any external input to charge.

This, of course, is assuming Im not completely confused on what you are trying to accomplish. I apologize if I am.

J.

 

I guess the alternator does have two wires going to it. I can figure out what to do with the battery cable that goes to the stud on the back of the alternator. That's an easy one I think you pretty much answered my questions Justin, thanks! I'm probably going to run the red wire (with resistor) to an auxiliary fuse block that I'm running my fuel pump relay, fan relay, and some other things off of.

 

so if we arent using a pcm we need to somehow get 5v for the red wire going to the alternator? we are using the truck alternator also if that makes a difference.

 

The truck alternator is different from the Fbody alternator. The truck alternator plug has 2 or 3 wires in it opposed to the 1 wire in the Fbody plug. I don't remember which wires you use in the truck plug, but I'm pretty sure you'll be able to find something on LS1tech about it.