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Bypassing electrical distribution block on M50 swap

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    #1

    Bypassing electrical distribution block on M50 swap

    I'm in the middle of swapping an M50NV (using an E36 automatic harness that I deleted all the auto tranny stuff from) into my 7/86 325e 24 Hours of LeMons race car. This is a completely gutted car with no dash or interior and no electrics inside the car other than gauges and light/wiper switches.

    Part of the job includes installing (actually relocating) a 4 post electrical kill switch in a custom made panel in the middle of the dash area. Rather than using the stock battery cable (big and small gauge with fusible link) from the trunk to the power distribution block on the firewall, I am using my own cables (including a smaller 10-gauge wire with a fusible link for the fuse box) that goes from the battery along the trans tunnel straight to the kill switch.

    Rather than going from the kill switch to the distribution block, I wanted to eliminate the dist. block altogether, and route the cables from the kill switch straight through the firewall (using the old heater core hole) and right to the starter, plus the stock E30 fuse box wires.

    Seemed like a good plan until I noticed a cable on the passenger side of the M50 harness near the diagnostic connector which I believe needs to connect to the dist. block for power. Specifically, it's the one circled in this photo (stolen from another thread).



    From the research I've done, the one closest to the diagnostic connector is a ground (attached to the strut tower in this photo), and the circled one is 12V for the harness. I cut the insulation off and one was red and the other is brown, so red should connect to 12V, and brown to ground, correct? I already removed the large gauge E36 starter/fuse box cable altogether since it's redundant when using the E30 cables instead.

    Based on this, I reinstalled the dist. block on the firewall only to use as a junction point for the small gauge wire to the fuse box. So I've got a small gauge wire running from the output side of the kill switch to the dist. block (running through the ECM wiring harness grommet), where the above mentioned power wire to the M50NV harness AND the two E30 fuse box wires are connected. Is there any reason this won't work?

    Also, does anyone know what kind of amp draw the main large battery cable has? I'd like to add a maxi-fuse or circuit breaker for extra protection but don't know how large it should be.
    The Homer: Powerful like a gorilla, yet soft and yielding like a Nerf ball.
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    #2
    why not run your kill switch between the power cable and the distribution block? seems like it would be far less painful.

    does it just have to shut off the engine, or does it have to kill all power? I imagine the kill switches have some pretty big posts inside to be able to hook to the battery cable?

    the amp draw is going to be HUGE. that main power is for everything, including the starter.
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    Bimmerlabs

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      #3
      that looks like the dme power wire. which is gonna power all the relays and the computer

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        #4
        Originally posted by nando View Post
        why not run your kill switch between the power cable and the distribution block? seems like it would be far less painful.

        does it just have to shut off the engine, or does it have to kill all power? I imagine the kill switches have some pretty big posts inside to be able to hook to the battery cable?

        the amp draw is going to be HUGE. that main power is for everything, including the starter.
        The original thought was to only need a cable from the kill switch to the starter. By going through the firewall in the heater core hole and bypassing the dist block, the overall run would be much shorter. But that plan went awry when I saw the DME power cable.

        The kill switch has to kill ALL power which is why I am running both the large and small battery cables through it.
        The Homer: Powerful like a gorilla, yet soft and yielding like a Nerf ball.

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          #5
          Bottom line is I have already done the work... I just want to make sure this will work properly. The E30 fuse box wires and the DME power cable are getting power, and that's all that matters, correct?
          The Homer: Powerful like a gorilla, yet soft and yielding like a Nerf ball.

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            #6
            Just in case anyone was wondering, this set up worked fine. Car fired up perfectly.
            The Homer: Powerful like a gorilla, yet soft and yielding like a Nerf ball.

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              #7
              What about the alternator ? You'd still have some power going to the fuse box and the DME if you're in gear. that's if I understand your first post correctly that you installed the kill switch before the junction box.

              PS isn't it way above budget for a lemon car ? I thought there was a $500 limit
              Sticky:True e36 one touch windows DIY

              1990 M3
              1992 Mtech (S50 + 5 Lug)

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                #8
                Didn't see this... you're correct, if the driveline over-drove the engine, the alt could feed power, however I would only ever kill power once the car was actually stopped.

                This will be the 6th LeMons race for this car. Blew a head gasket (at least) on the old eta M20, and found a former LeMons E30 racer that had this M50 swapped in. The body was trashed and wouldn't pass tech, so they sold me the whole thing, running and driving, for $250. Assigned residual value after previous race, plus selling some parts = legit for $500 budget.
                The Homer: Powerful like a gorilla, yet soft and yielding like a Nerf ball.

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