Altenator wire with resistor

[tphsmith]

yes I found a topic in the FAQ's but im a dummy. so this resistor controlls feedback of power in the wire from the instrument cluster to the altenator? but if you have an idiot light you dont need the resistor?. but ok here is my dummieness, this light in the instrument cluster ? is this the Alt light or is it something else. sorry to be soo stupid on black friday but I'm trying to clean up the wireing mess I have in my 72. and if this resiistor is needed is there a specific way to put it in line of the wire. it seems like once apon a time i read where the color band on the resistor needs to be on the side (direction towards) of the altenator?

[JimKshortstep4x4]

The stock wiring on the trucks have a resistor wire that routes from the ignition switch to the voltage regulator and to the alternator. When the ignition is turned on the alternator is "excited" by the low voltage (6-8 volts because of the resistor wire). This causes the alternator to charge with the engine running.

Unless you are replacing the wiring the resistor wire should be intact so no change is needed.

However you mention a "band" around the item that you are wanting to install so I wonder if you are not putting a diode in the system, (which is not needed for the stock system).

If you are not going back with a stock charging system, let us know what you are trying to do.

Jim

[tphsmith]

yes I should have added alot more detail I am adding a 150 amp alternator in my 72 truck and I have been going threw my wire harness and because of my ignorance I deleted the wire in the harness off the bulkhead that had this resistor. the wire was brown and it went to the old voltage regulator and without understanding whet that was soldered into this brown wire I took it out. now Im back working on the same wire harness and I am worried If I need this resistor in the wire that I will have going to the alternator from the bulk head for the Alt idiot light in the gauge cluster. PLEASE SomeOne teach me what I dont know

[tphsmith]

can someone help me out

[VetteVet]

It appears to me that you have one of the newer style CS alternators. They are much better tha n the older external regulated original style that came on our trucks.
In order to properly make the conversion you need to know how the older system works.
JimK detailed the part that the brown wire plays in the stock system and how the idiot light is necessary for the resistance that the alternator internal regulator needs to prevent burning it out. The light is the actual resistance that the brown wire has in the original system and it must be used in order for the alternator to work properly and to keep the warning system in the dash. It is possible to eliminate the warning(idiot) light but a resister must be substituted in the wiring circuit at some point. If memory serves this resister will be on order of 75 ohms and 3 watts. That is probably what you have and it does not matter which direction the current flows through it. The color bands are the identifiers and give the value of resistance.
You probably have the newer style CS alternator and you can use it with or without the
idiot light, but if you don't use the light then you will need to use the resister. There is a
small adapter wiring harness mentioned in the website below that will enable you to do this. It is in the second part of the article and be sure to read the notes.
If it was me I would just replace the brown wire you removed and wire the new alternator like the website shows. You wouldn't have to wait for the harness or make one and your idiot light would work as it should.
One point I wanted to make is that there are two brown wires coming from the bulkhead connecter. One is the long wire to the old voltage regulator and the other goes to the brake proportioning valve. It is shorter and may be a lighter color brown.
Post more if you need more help and I hope I haven't confused you too much.

http://www.chevelles.com/techref/tecref14.html

[tphsmith]

thank you guys, VetteVet I had that topic of the chevelle pulled up, this is the wire that went to the old voltage regulator that I have eliminated because of this new alternator from a corvette, hence installing a LT1 in the 72. but the truck had a internal voltage regulator on the truck when I bought it and I was making things real difficult because the brown wire out of the bulk head had not been replaced when they by-passed the voltage regulator so ] was in panic mode if I still needed the resistor in line of the wire even though I was still hoping to use the original idiot light in the gauge cluster