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    Wiring Confusion

    I have been in the process of (slowly, it seems) converting my '86 eta to 325i specs. My latest hurdle is the wiring.

    The engine harness is from the '89 donor car, and I ran into some differences under the dash I was not quite expecting. I knew the idle control module in the '86 would become history, of course. My problem centers around a 3-pin connector under the dash of the '86 which connects to the engine harness.

    Here is what I have on the '86. The colors refer to the different wires.
    3-pin connector
    Car side of connector: Black, green, yellow/white
    Engine harness side: Big green, little green, yellow/white

    1-pin connector
    Car: Green/black
    Harness: Blue/white

    The 3-pin connector in question is, I think, C105. I connected my VOM to the larger of the green wires on the harness and found that it appears to be the power supply to the ignition coil. The other two wires on that connector are a complete mystery. I think I've figured out the single-pin connector goes to the park-neutral safety switch.

    Now for the '89 connectors.
    White 3-pin connector (C131?)
    Car: Green/black
    Harness: Brown, green/violet, red/blue

    The green/black wire connects to the red/blue wire.

    Black 3-pin connector (C136)
    Car: Black/red, black/violet
    Harness: Violet/gray, black/gray

    Black/red connects to black/gray and black/violet connects to violet gray. Near as I can tell, these wires are all associated with the air conditioner.

    I used the online Electrical Troubleshooting manuals for my information, but while the '89 manual is quite usefull, the manual for the '86 is not much help at all.

    So, I need help. I knew I'd run into some issues, but this has me pretty much buffaloed right now.

    #2
    The first connector mentioned (with the black, green, and yellow wires) is C104. It was only used on cars produced before 9/87. The green wire is the START signal supplied to the DME from the Hot in Run and Start circuit. The black and yellow wires are the tachometer and econometer outputs respectively from the DME. From 9/87 on those signals were routed through C101. You'll have to salvage the connector from 86 harness and graft it in or route those wires through C101.

    Pin 20 of C101 may be grounded on the body side. Your 89 harness will have that pin connected to the main relay and if you don't cut the wire to pin 20 you'll smoke the harness the first time the main relay closes. Cut it on the body side.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

    Comment


      #3
      Originally posted by jlevie View Post
      The first connector mentioned (with the black, green, and yellow wires) is C104. It was only used on cars produced before 9/87. The green wire is the START signal supplied to the DME from the Hot in Run and Start circuit. The black and yellow wires are the tachometer and econometer outputs respectively from the DME. From 9/87 on those signals were routed through C101. You'll have to salvage the connector from 86 harness and graft it in or route those wires through C101.

      Pin 20 of C101 may be grounded on the body side. Your 89 harness will have that pin connected to the main relay and if you don't cut the wire to pin 20 you'll smoke the harness the first time the main relay closes. Cut it on the body side.
      Just to make things clear, the '89 is the donor car, so anything salvaged will come out of that. I'm putting all this into the '86.

      Now, if I cut the ground to pin 20, how will that affect power to the main relay?

      If possible, I'd like to route as much as possible through C101 and make this as clean an installation as I can. I've messed with too many buggered-up electricals, such as the mess I'll be cleaning up where the C191 connector was, (That is going to be replaced with a WeatherPack connector.) to want to mess things up even more. Besides, I'd like to keep this little car awhile, so I don't want to be faced with cleaning up my OWN mistakes later on. :ohsnap:

      I did some more research on this last night, and I see this is a common problem among those dropping an M50 into their E30s. Frankly, I'm glad I'm not going that far on this project. I'm growing fond of the M20 engine.

      You answered this same (more or less) question for me on Bimmerforums, didn't you?

      Comment


        #4
        My next challenge will be figuring out how to make the connections between C136 on the '89 harness to the A/C controls on the '86. :crazy:

        I just took a quick peek at C101 on the '86. There is a wire at 20 in the engine harness, but it is empty on the car end of the connector.
        Last edited by Three Dee; 09-02-2012, 12:50 PM.

        Comment


          #5
          You can get the pins for C101 from you dealer and route the START, tach, and econometer wires through C101. In one sense that is the best solution since you can then use any engine harness from 9/87 on. But there is nothing wrong with adding C104 to the harness you have.

          There doesn't seem to be any fixed patter for pin 20 of C101. I've seen early cars where that position is empty and early cars where it is a ground. As long as it isn't a ground there will be no problems. Pin 20 was part of of the SRS system on very late production.
          The car makes it possible, but the driver makes it happen.
          Jim Levie, Huntsville, AL

          Comment


            #6
            Originally posted by jlevie View Post
            You can get the pins for C101 from you dealer and route the START, tach, and econometer wires through C101. In one sense that is the best solution since you can then use any engine harness from 9/87 on. But there is nothing wrong with adding C104 to the harness you have.

            There doesn't seem to be any fixed patter for pin 20 of C101. I've seen early cars where that position is empty and early cars where it is a ground. As long as it isn't a ground there will be no problems. Pin 20 was part of of the SRS system on very late production.
            By the way: Am I to assume that since there is no pin at 20 that the main relay circuit is not only safe, but will get power?

            Comment


              #7
              Yup, the main relay gets power on a different pin. The pin 20 thing is ONLY for the airbags.

              2/87 had pin 20 to ground on the body side, so make double sure there's no body- side ground.

              Then you're fine- Jim's advice to put tach and vss into the body side of the connector's
              a good idea.

              t
              now, sometimes I just mess with people. It's more entertaining that way. george graves

              Comment


                #8
                Thankfully, neither car is an airbag car (I know the '86 would not be, in any case.). I know the '89 isn't because the horn button was still in place, even though the car itself is a twisted mess after the accident it was in. Fortunately all four occupants walked away from the accident, and the previoous owner is mighty glad of that because his daughter was at the wheel when the semi forced them off the road.

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