12V Disappears at Starter??

[EyExR]

I'm having a problem getting my starter to crank. When testing for power I'm supposed to get 12V at terminal 50 when the key is in the start position. I don't.

What's very strange is that when I disconnect the wire from the terminal and test the wire I get 12V at start then also position #2! ??? Then as soon as I reattach it to the terminal the 12V disappears. I'm stumped.

The starter does work though. I jumped terminal 30 and 50 and the car starts right up.

I've been told this is called backfeeding but I don't know how that works.

I will be testing the C200 connector from the ignition switch next. Then I guess I have to start testing my wiring harness as well..

But any insight here would be greatly appreciated it. I want to use my key again! :)

edit: I forgot to mention that I have continuity from Pin 27 at the ECU and the black wire at terminal 50...

[EyExR]

Ok. Maybe I'm getting somewhere?

I found this on the M3forum: "could be BMW grounds this connection and has a hot solenoid coil (as discussed above.) Check for this with an ohmmeter - or a test lamp (safer probably) - hook 12V test lamp to 12V source (red wire) and other end to black wire - and try the key/clutch deal. If the light comes on brightly - they used this wiring scheme. If that isn't the case - and 12V is just missing there - the question is why? Well - the EWS system might disable the starter, so that's a possibility, or your ignition switch could be bad, or your clutch switch could be bad." -deilenberger

I don't have a test lamp. Does anyone happen to know what the resistance is supposed to measure?

[AndrewBird]

Power goes from the ignition switch to the starter relay, then to terminal 50 on the starter. So you either have a bad ignition switch, a bad relay or power is not getting to the ignition switch.

Start by check for power into the starter relay and then after the relay. If you have power before but not after, then the issue is the relay or the trigger for the relay.

I would also buy a test light. They are like $5 at any auto parts store. Using a meter can give you false positives with "ghost" power. Meters are used for measuring the amount of voltage, not whether it is there or not.

[StereoInstaller1]

There is no starter relay. Black or black/yellow (BTW: German is SW/GE) goes from the ignition swithc (autos do other shit) straight to C101, then to the starter. Its either black or black/yellow.

If your car has the later unloader circuit (that prevents power to the HVAC fan and windows during crank) there is also a smaller green/black attached to the smaller starter terminal.

If that part is wrong, you won't have working power windows or fan, but do't panic, just ground that terminal for testing.

If you have the earlier unloader system the start wire (again, that black/yellow or black) will show about 9V when key on and show 12V when cranking.

Hope that clears it up for you.

Luke

[EyExR]

There is no starter relay. Black or black/yellow (BTW: German is SW/GE) goes from the ignition swithc (autos do other shit) straight to C101, then to the starter. Its either black or black/yellow.

If your car has the later unloader circuit (that prevents power to the HVAC fan and windows during crank) there is also a smaller green/black attached to the smaller starter terminal.

If that part is wrong, you won't have working power windows or fan, but do't panic, just ground that terminal for testing.

If you have the earlier unloader system the start wire (again, that black/yellow or black) will show about 9V when key on and show 12V when cranking.

Hope that clears it up for you.

Luke

Thanks, Luke! Very helpful.
I know my ignition switch is working after doing a continuity test at C200. And I have continuity from the pin27 on the ECU to terminal 50... I also reseated the C101...
This is a 1991 so perhaps it does have an unloader system...? I broke the wire to the small terminal on the starter when removing the harness so maybe I overlooked a second wire.? I'll take a closer look.

[AndrewBird]

I was looking at the ETK for an 89 and it shows a starter relay. However, looking at it closer, it appears to only be on auto cars and is a lock-out to prevent cranking if you aren't in park.

[EyExR]

^Thank you

Luke was right! I pulled the harness and found a second smaller wire tucked in there. Re-wired it and I'm back in business. Thanks!