Alternator Wiring Question

Discussion in 'The Garage' started by Beards88, Jun 24, 2004.

  1. Beards88

    Beards88 Registered Member

    Oct 16, 2002
    Likes Received:
    Austin, TX
    I have an 86 Blazer that had the old SI series alternator (2 wire plug). I dropped an 89 motor in it with the CS alternator (3 wire plug). I replaced the plug but it has the extra brown wire on it. According to Chiltons the brown wire goes to the indicator light, so I left it off since I have a Volt guage. The alternator does not charge the battery this way. The current plug wiring is:Black-ground, Red-12V, brown-disconnected. Does anybody know how this should be connected? The current alternator is brand new. Thanks for the help.
  2. diesel4me

    diesel4me 1 ton status Premium Member

    Jul 24, 2003
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    The brown wire on the older altenator(1986)was the one that energized the field to make it charge--it sends power from the ignition switch through the idiot light or gauge to the altenator--the other small red wire is hot all the time,as is the large red wire that has the stud and nut terminal-- I dont know the exact differences on the newer style altenators,but from your description it sounds like the newer one just has the black wire for ground,and the other two do the same as the old altenator.But I'd wait for someone else who has more experience with the newer rigs--I only know how the dinosoars I drive are wired for certain,I dont want you to blow your new altenator up because I was wrong! /forums/images/graemlins/blush.gif
  3. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

    Apr 20, 2004
    Likes Received:
    Northern Colorado
    This is the info I used. Worked great. /forums/images/graemlins/waytogo.gif

    [ QUOTE ]
    Most of the connectors for the CS alternators are four wire but will only use two of them and the wiring is the same as the SI.
    · S = a heavy gauge wire to the battery supply (horn relay)
    · F = not used
    · L = a small gauge wire that comes from the idiot light and energizes the alternator
    · P = not used
    You need to purchase a conversion adapter that is just 2 short wires and 2 connectors. One is a CS connector to plug into the alternator, the other is a female connector to accept the SI plug from your original harness. There are two different types of conversion adapters. One is a non-resistor and the other has some resistance built-in it. The "L" wire that energizes the alternator needs some resistance (35 ohms or more) in it otherwise it will cause the alternator to fail. If you have a warning light in the dash then that bulb serves as the needed resistance and you should use the non-resistor adapter. If you don't have that bulb or have less than 35 ohms resistance in the "L" wire then you will need the adapter with resistance built in. If the "L" wire has more than 350 ohms then there is a problem with that wire and it will need to be fixed.
    Non-resistor adapters:- AC Delco: 8077- Haywire: 2110- Painless Wiring: 30707 Resistor adapters:- AC Delco: 8078

    [/ QUOTE ]

    I had problems because the dual battery isolator couldn't handle the higher rated alternator.

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