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Electrical Gremlin (car wont turn off)

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    Electrical Gremlin (car wont turn off)

    First of all, I'd like to say I appreciate your help. I know this is a bit of a shit storm, but any advice would be appreciated.

    I have been Knee deep into this project for a couple of years now, working on it at random when I have time. The car hasn't been driven yet and has only been run for 5 minutes half a dozen times. Turned out to have lots of random issues and I made the mistake of doing a motor swap and turboing it before fixing them. So I'm now on a megasquirt base tune and I'm trying to figure everything out and get it running enough for my tuner. Been hitting so many roadblocks it ridiculous. It seems like a dozen teenagers owned this car at some point because its a rats nest in too many places to count.

    I hadn't touched the car in a couple of months and realized that I killed my battery. So I bought a new battery and found the drain from fuse 21 when the ignition is off.

    Question number 1: Is it possible that I killed those si batteries because random stuff on my cluster doesn't work.

    Now here comes the real mistery. I found out that my alternator wasn't charging my battery after I did the motor swap. So after doing some testing, I bought another one at the junkyard for $30 and swapped it in last night. Afterward, I checked the voltmeter and it seems to randomly pop up to 13 volts kinda rhythmically, but not enough to maintain the proper voltage on the battery. After I got done tinkering with this for a couple of minutes I go to turn the car off and it doesn't turn off! At first, I was terrified, because I hadn't bled the coolant yet, so I was concerned it was detonating due to heat, but it was running for a very short period. So I waited about 20 minutes, turn it on and off quickly, no problem. Turned it on again waited 1 minute, didn't turn off. Same issue. So I was curious if it would run without my battery hooked up and to my surprise, it did run while my battery was completely unhooked.

    I know this is a long read, but I'm baffled.

    Plan of attack:
    1. Right now my game plan is to check the grounds and alternator connections after work.
    2. Figure out if my cluster is interfering with the car not shutting off and if the SI batteries my be part of the problem.

    Any words of wisdom here guys?


    Checked these off the list for battery drain on fuse 21.

    Here is the wiring diagram for the alternator.
    Click image for larger version

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    Last edited by Yuri; 07-22-2019, 11:03 AM.


      First, I would think your parasitic drain and ignition issues are unrelated.

      Ignition issues: Investigate the exciter circuit. If it back feeds (assuming the charge light is working), the charge light will illuminate when you turn the key off. It keeps the relays active and won't shut off the engine, obviously. I had this happen to me when I rewired my megasquirt setup for MS3x. I didn't investigate, just threw a diode in line with the charge indicator--actually replaced it in fact. You can see it happening here:

      The easy way to diag if this is happening to you is to eliminate the circuit by unplugging the C1 connector on the cluster. This will also be another way for you to eliminate one branch on your parasitic drain issue(same plug).

      Re: parasitic drain - How many milliamps is it pulling? 200? 500? 1A? Looking at the diagrams, Fuse 21 goes into the cluster to "memory power input" and goes out of the cluster to the "OBC, multifunction clock" according to the diagrams for an 88 325. There are some differences between the years, so knowing your year/model would be good.
      '84 318i M10B18 | 93whp/90ftlbs | 147- Safari Beige | MS2E w/ LC, 2-Step


        Yes, your SI board batteries are dead if they have never been replaced. They are 30 years old, there is no such battery that can last that long. When the batteries drain, they will rapidly switch power the SI board causing failure of the capacitors and transistors so replacing the SI board batteries alone will not repair it. The entire SI board must be refurbished.

        The smaller wire going to the alternator is not dropping to zero volts when the key is turned back, if this wire remains powered on, the vehicle will continue to run.

        This can be cause by a short in the cluster or in the cluster harness or somewhere else along the path to the alternator.
        Owner - Bavarian Restoration
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          Really appreciate the help guys, I'll keep you posted after I look at it this weekend.


            Alright here is an update. I Just ordered a new SI board from FCPeuro. and I'm hoping that fixes some of my instrument cluster issues. Apparently, because I have a 5/87 325is I cannot update the si board to the batteryless boards.

            But here is the main issue I am having regarding the car starting and not turning off/not turning on. When I unplug the small blue wire (B+) connected to the alternator the car turns on just fine; however, when I put the blue (B+) wire back on it doesn't start, blows a relay and I have to wait a couple of minutes before I get any power back anywhere. Also, when the cars relay switches back on, it shutters ever few seconds and clicks while my dash lights flicker dimly.

            Originally the blue wire connection was damager so I resoldered on new fitting. When I have the car in acc, the battery light is on with the cable connected and off with it disconnected. Not sure where to go from here. Read through the manual and still haven't found my answer.

            This is just a crapshoot for me gents.. What do you guys think? my next step should be?


              Turns out the alternator that put in was actually bad. it was shorting out the entire system. Replaced it again and the problem is solved.