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226 PMU 16 - wont go off when engine running

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hi all

started my setup yesterday the first time. Engine running fine...

however: the PMU wont go off when the engine is running.

Strange: when the engine is not running and I turn Ignition Key off, the PMU shuts down as it should.

When I did start the engine and turn ignition key off, the PMU keeps working and so does the engine since my ECU is connected to the PMU.

Thats not how it should be. Any hints?

Does the alternator output go through the PMU so it can be disconnected? (the other reason to do this is to monitor the current provided by the alternator)?

Or do you have your alternator output connected to the battery directly, so that only power to the ECU / Ignition comes through the PMU

so i found the problem or the issue - but i have no clue whta is going on. always thought i something about automotive electri but now i am lost.


Car is a BMW e28 -> engine swap M50 from e36

ECU: maxxecu + PMU 16


PMU16 gets ignition switch directly from KL15 (ignition switch steering column)

I also did replace the original instrument cluster by a Bosch dash display.

Important: charging bulb is now an LED with a parralle 3W resistor

Whats happening:

without engine running I can shut down everything by turning ignition switch on/off

when I start the engine -> charging bulb goes off -> engine runs

when I try to turn off the engine, the alternator starts to supply the ignition switch leads with power via the charging bulb -> so PMU will not shut down since it gets still power supply on PIN7.

if I take off the charging bulb, I can turn off the engine with the ignition switch but of course, the alternator is not charging the battery.

Strange thing is also, that even with the serial instrument cluster, the engine is not to stop when turning off by the key.

So I am really lost, since I do understand what is happening - but I have no clue how this could or should ever work even in a serial production car.

(Of course I could program easily a switch in the PMU to turn off but it has to work also with the standard ign key)

totally lost - need your help!


You should connect the Ignition KL15 to the ECU as well as the PMU. The ECU should be configured for a RUN/STOP, Enable, or Ignition Switch function. This will allows the ECU to stop running the engine when it sees the ignition has been switched off (even if it's still getting power). When the engine stops, so will the power from the alternator.

Hey David

Thanks for your help.

Unfortunately this would not make sny difference since ecu will not notice that ignition key is turned off since it still gets power on kl15.

Thats my main problem: when the engine is running i cant shut down kl15. So any device connected to kl15 stays on.

Never ever experienced something like this

I've seen plenty of race cars with an incandescent bulb wired to the charge light circuit up under the dash, or in the engine compartment. I think your replacement of that bulb is the problem.

I thought aswell

But even using the original cluster with original wiring - same problem now. Engine will not shut down

I thougt of putting a diode in the circuit behind the bulb...

But it must work without

Looks like most people in this forum are struggling getting the engine to start. Well i am probably the only one with the opposite issue :)

i did attached a picture of the circuit - at the green mark i did connect the switch to the PMU (Pin 7)

Attached Files