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    Alternator wiring modification.

    I was just looking at some old pictures of the engine I took out of my parts car and couldn't help but notice how small the wires for the alternator are!.



    The + looks like 8-6ga, and the - looks like 12-10ga. Seems to be overly small, especially considering its low strand count crappy wire. Considering that at any time up to 90+ amps are trying to flow through that wire..... bigger could make a noticable difference.

    Has anyone ever replaced it with like a 4ga + and 8ga - (car stereo wiring) leads before?

    I'm pretty sure the + lead just runs through the main engine harness, and terminates at the junction block above the battery tray, but I'm not sure where the - lead terminates. Anyone know?
    Tenured Automotive Service Professional - Avid BMW Enthusiast

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    #2
    the Main Red wire goes threw the harness then the other end attaches to the 13mm post on the starter.
    85 325e 2.7 ITB'd stroker

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      #3
      Oh awesome. Thats a nice short run. I definately have enough 4ga red power wire to make that run.

      any idea where the negative lead goes?
      Tenured Automotive Service Professional - Avid BMW Enthusiast

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        #4
        Originally posted by Jordan
        any idea where the negative lead goes?
        Couldn't you just run a 4 ga right to the frame rail? I think there is a ground strap there already.
        '91 318is
        sigpic

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          #5
          Originally posted by Brew
          Originally posted by Jordan
          any idea where the negative lead goes?
          Couldn't you just run a 4 ga right to the frame rail? I think there is a ground strap there already.
          If the lead just terminates to the body somewhere else, yes I could. But I need to make sure that is the case first.

          I could go outside, pop my hood, poke around and try to see... but its cold and dark.
          Tenured Automotive Service Professional - Avid BMW Enthusiast

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            #6
            Originally posted by Jordan
            If the lead just terminates to the body somewhere else, yes I could. But I need to make sure that is the case first.
            Well, it is a ground, so it has to terminate at the body or at the negative terminal of the battery at some point.
            '91 318is
            sigpic

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              #7
              It looks like it may also terminate at the starter motor. Can you confirm Ely?
              Tenured Automotive Service Professional - Avid BMW Enthusiast

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                #8
                it depends on the starter you have. Is it a big case or a small case? (2 or three wires coming from the starter?)

                NASA MidSouth TT Director / GTS2 #018
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                  #9
                  This is the starter/wiring configuration I used in my car (prior to being cleaned up)

                  Tenured Automotive Service Professional - Avid BMW Enthusiast

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                    #10
                    the smaller bundle of wires goes to the instrument cluster for the Battery light. The ground for the alternator is threw it's case or some have an external 3" wire that grounds to the engine block.
                    85 325e 2.7 ITB'd stroker

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                      #11
                      Most alternator grounds ground at the engine block, and the chassis. I think the alternator on mine grounds to the chassis just inside the d/s front wheel.

                      Will
                      RIP e30 (brilliantrot '91 325i) 11/17/06 Byebye: 8/21/07
                      Welcome e30 (brilliantrot '90 325is) 12/23/06
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                        #12
                        Having a charging problem? or just wan't to make sure 100% output ? what battery are
                        you using ? Lights dimming? I bet they do if you run full lights and system cranked !
                        A cap and or Optima battery would help. When ya get a chance , I still would like to know how you run full lights, or fogs only on are cars, 06/87 build date. thanks Jordan ...
                        John Hubbert

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                          #13
                          I have been thinking about doing this for a while. I got great info here:



                          Thanks for starting this thread Jordan!

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                            #14
                            Originally posted by Hubbert
                            Having a charging problem? or just wan't to make sure 100% output ?
                            No charging problem, just want to make sure everything is 100%

                            Originally posted by Hubbert
                            what battery are you using ?
                            Factory spec Exide battery (huge one)

                            Originally posted by Hubbert
                            Lights dimming? I bet they do if you run full lights and system cranked !
                            Nope. I can have the system at max, all 6 lights on, car at idle. No dim.

                            Originally posted by Hubbert
                            When ya get a chance , I still would like to know how you run full lights, or fogs only on are cars, 06/87 build date. thanks Jordan ...
                            Sorry man, I forgot about that. I will PM you soon with the info.
                            Tenured Automotive Service Professional - Avid BMW Enthusiast

                            Vapor Honing & E30 ABS Pump Refurbishment Service
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                              #15
                              It's not a - or ground wire. It's a field wire and it also triggers the warning light in the dash. Don't mess with it, it doesn't carry much current.
                              Adam Fogg- '88 M3

                              Common sense- It's the new 'gifted'

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