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    Main power relay?

    Hey everyone. I have finally gotten around to committing myself to get my megasquirt wired in. To make my life a little easier, and because I am adding some extra things to the car (and removing some others). All of the HVAC controls are going away, radio is being deleted, obc panel, etc. the car is being turned into a track car, and I am putting a switch panel in place of the dash panel.

    The idea being I will have a main power switch, push start button, a fuel pump switch, a manual override switch for the electric fan, accessories 1 and 2, and potentially find a way to add the potentiometer from the HVAC control so I can turn the fans on in case the window fogs.

    The issue I am running into now is I am not sure where the e30 fuse box is getting it's switched power from. I do not see a main relay anywhere on any fuse box diagram, so I am not sure at this point where to tie the main power switch into.

    I would love some feedback form anyone who has done something similar to this or can provide me some useful feedback.

    #2
    just rewire the column keyed ignition tumble to switches instead to suit your needs?
    '89 325i OBD2 S52 BUILD THREAD
    Shadetree30

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      #3
      Originally posted by Sh3rpak!ng View Post
      just rewire the column keyed ignition tumble to switches instead to suit your needs?
      That's the solution I have for now. I was just hoping to figure out if there was a main relay, or if every relay in the box just fed off the ignition switch. It just seemed like it would have been easier if there was in fact a main power relay for the box.

      Part of the confusion is coming from merging 3 separate wiring harnesses together at this point (megasquirt, obd2 m52 harness, and e30 body harness through c101)

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        #4
        There is no main relay. There is straight cable from battery to fusebox. No big main fuse or relay. Wire c101 as in any m52 swap and wire megasquirt to the m52 dme connector. Easy and no drama :D

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          #5
          Originally posted by pazi88 View Post
          There is no main relay. There is straight cable from battery to fusebox. No big main fuse or relay. Wire c101 as in any m52 swap and wire megasquirt to the m52 dme connector. Easy and no drama :D
          Luckily I already wired in the c101 a while ago. Hopefully I did it right ;)

          Comment


            #6
            I have done several race car harness conversions.

            There are actually only 4 or 5 wires at the c101 that is needed for the engines to run with stock engine harnesses (not taking gauges and accys into consideration).

            Wires needed for running conditions to be met:

            Ignition on power to big green wire (engine side, it's yellow stripped on the chassis side of some cars) is power to ignition coil(s) (pin 7 c101, pin 21 on x20)
            Starter switched to big Black/yellow wire is starter engage (pin 18 c101, pin 18 on x20)
            Power to big green/purple fuel pump engage (pin 13 c101, pin 13 x20), which comes from fuel pump relay
            Blue wire is alternator exciter wire. This goes through the dummy light in the cluster (or can just use a 10ohm resistor to key-on power) (pin 1 c101, pin 25 on x20)

            These 4 will make the engine run with a stock 24v (or even m20/m42) harness.

            To get the 02 relay to kick, you will need ignition on power on the green white (or yellow) (pin 6 on c101, pin 22 on x20) - but isn't required for engine to run - you most likely will have a WB o2 feeding back the MS, so unless you power the WB from the stock o2 relay, this may not even be needed in your case.

            The rest of the c101/x20 wires are accys, gauges, check engine etc.
            john@m20guru.com
            Links:
            Transaction feedback: Here, here and here. Thanks :D

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