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Double Check - Ignition Key Switch fried???

Before I go through the ugly task of replacing the ignition switch in my 1988 930, I thought I would check to see if my logic makes sense.

Re-installed engine/tranny. complete with new wiring harness, alternator regulars. Previous harness melted (long story).

Went to re-start and the starter would engage but would keep running, even with the key pulled out! Had to disconnect battery.

Test:

Using heavy wire, jumped between terminals on solenoid (+ve from battery and yellow from ignition. Did NOT take yellow ignition wire off terminal post). Starter fired but ran continuously even with jumper pulled.

Removed yellow wire that comes from ignition switch to solenoid. Just jumped from battery +ve to the terminal where yellow was attached. Starter turned and would stop when jumper pulled. Could even start and run engine (JOY!!).

This says to me that once energized, the ignition switch "sticks" and causes the solenoid to drive the starter.

Conclusion: Replace the ignition key switch electronics.


Does anyone see anything wrong with this logic??

Thx.

Old 11-05-2014, 08:00 AM
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not so far but you can test some more.
what wires do you have going to the starter? batt and alt on large post, yel wire on one post and you should have the power to the CSV on another post.

what i am thinking is you may have enough power getting on the yel wire to keep the solenoid egaged but not enough to pull it in on its own.
pull the yellow wire and with the key off measure volts on wire from wire to ground. you should have 0volts. (or use a test light). if the light is on, disconnect connectors until the light goes out working your way back to ignition switch.
the drawings i have are not clear enough for me to trace the signal but porsche uses the starter as a ground path of other things. i am looking into the above part some more.

or:
connect yellow wire back up. remove 14 pin connector at relay panel. (make sure it is connected correctly first. i think i put one on one set of pins off once). run test again.

i show 2 other connectors the yel wire goes thru. you could either test it disconnecting each connector or after doing the 14 pin connector(easy test) just goto the ignition switch and remove yel wire and jump starter..
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Old 11-05-2014, 08:41 AM
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i cant read the 88 drawings at all. they are too washed out. its hard enough to read the 86 ones but it LOOKS like the AC relay uses the yel wire as a ground.
looking at the 87 it looks like some other stuff may use the solenoid as a ground.
may be one of these items is drawing too much current making the solenoid stay in.

(i wonder if they use the solenoid as a current limiting device. just a thought).
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Old 11-05-2014, 09:40 AM
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Unplug the harness from the back of the ignition switch.
Jumper Pin 30 (RED - Main Power) to Pin 50 (Yellow - to starter solenoid)

This should engage the starter, does it? and does it disengage when jumper is removed?
If the above test works you most likely have a bad switch.

And as already mentioned remove the AC relay as well and retest, since the AC relay gets it ground from (via) the starter solenoid. The reason it's wired this way is so that the entire AC system deactivates during cranking to help give max amps to the starter.

Also you don't need to remove the entire mechanical ignition switch. You can remove 2 screws from the back of the dash that hold the electrical portion of the switch to the mechanical portion. You need a 'L' shaped Philips screwdriver for this task. It's tight but can be done.
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Old 11-05-2014, 10:11 AM
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cant see how it does that when the AC relay is tied to the yel wire before it goes to the solenoid.
some cars do have "unloader"relays that are tied to a contact in the solenoid that opens when you start the car.
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88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 11-06-2014, 05:23 AM
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The AC relay's pick coil is actually grounded via the Starters solenoid. One side of the pick coil goes to the yellow wire that gets 12vdc power while cranking but when not cranking that yellow wire is effectively grounded via the Start Solenoid coil because that coil is very low resistance. You need to really study the circuit and you'll see how it actually will unpick the AC relay while cranking\starting.

Looks something like this

12vdc to activate AC relay
|
AC Relay pick coil
|
Starter Solenoid coil
|
Ground

Basically the AC Pick Coil is in series with the Starter Solenoid coil but the resistance of the Solenoid coil is significantly lower than that of the AC Pick coil so that most of the voltage is seen across the AC Pick Coil. But the minute the key hits 'START' then you have 12vdc at the top of the Solenoid coil and this now puts 12vdc on the bottom of the AC pick coil so that now you have 12vdc at both sides of the AC pick coil and that yields 0vdc across the pick coil and the relay deactivates. It's a very clever design simply based on Ohms Law of voltage drops across devices.

Try it: turn AC motor on full blast with key in 'RUN' engine off and then go to key 'START' and the AC will stop blowing. You can even measure at the AC relay or simply put your hand on it and you'll feel it click 'OFF' the minute you go to 'START'.

Quote:
Originally Posted by T77911S View Post
cant see how it does that when the AC relay is tied to the yel wire before it goes to the solenoid.
some cars do have "unloader"relays that are tied to a contact in the solenoid that opens when you start the car.
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Old 11-06-2014, 05:47 AM
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ah, got it. dont know why i did not see that. you made me think.
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Old 11-06-2014, 06:02 AM
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An update on the problem of starter engaging but not stopping even with key out.

Pulled A/C relay from front compartment fuse/relay box (?smugglers box). Starter still runs even with ignition key out.

Pulled off back of ignition key switch. Jumped pins 50-30. Problem remained. (so its not the switch.)

Question:

Should the a/c relay have been jumped to disengage the a/c? I swapped the a/c relay for another just in case it was a bad relay but the problem remained.

Any other ideas to try????

..J
Old 11-10-2014, 09:58 AM
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Didn't try pulling the 14 pin from back panel yet but will try that next.
Old 11-10-2014, 10:00 AM
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So it's not the ignition switch.

Something else is connected on that yellow wire that's feeding just enough current to keep the solenoid energized.

Not sure about the 930 but the 3.2L cars have a heat control relay at the rear fuse area that is also tied to that yellow wire. If you have that controller try disconnecting it. Also lower the 2 heat levers near the hand brake and turn the heat system totally off, also totally turn off the AC and test again.

We need a clear wiring diagram for that 88 930, look over the schematic for anything attached to that yellow wire.
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Last edited by scarceller; 11-10-2014 at 12:22 PM..
Old 11-10-2014, 11:40 AM
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I didn't notice if you suspected the starter in your diagnosis. I just had second Bosch reman starter replaced in seven years, with what sounds like similar symptoms. The faulty solenoid was failing to fully engage the starter gear, spinning the starter drive gear, but not pushing it into contact with the ring gear., key in, or out of ignition. To stop it, I had to disconnect negative battery cable. Bench test of starter reportedly confirmed this faulty starter solenoid issue.
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Old 11-10-2014, 12:48 PM
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did you pull the wires off the ignition switch?

start at the rear and remove the 14 pin connector then jumper the starter to start it. work your way to the front.

i think on the 911's they put the rear defogger on the starter solenoid, dont know about the 930.
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Old 11-12-2014, 03:10 AM
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Col 911. Starter ok. Was pulled and tested. Also will work fine when yellow wire off and starter jumped

T779911SC. Ignition plug pulled off and pins 50/30 jumped. Going to try the 14 pin plug suggestion next. I have a cab so no rear defog A real wiring diagram would be nice!

Thanks for ur suggestions
Old 11-12-2014, 05:16 AM
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either the 14-pin connector at the rear needs cleaning or has a bad connector, the yellow wire needs cleaning or bad connection at the starter, or this: does your car have an aftermarket alarm? This was my problem, and seems to be common with these cars.

Usually, the aftermarket alarm will be tied in to the harness that is connected to the ignition switch. Check that harness at the switch, and try to see where the newer wires are tied in to that harness (usually somewhere between the switch and the bulkhead connecter). Chances are, those wires are tied in poorly, which will cause a voltage loss.

The same where the alarm is located under the front hood. There are some tie-in's to the original system, probably either blunt-connected or worse, taped. This can cause the same issues you are experiencing.

It takes some time and patience.
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Old 11-12-2014, 05:46 AM
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Yes aftermarket alarms really suck.

If the wires were still connected to switch it could still be the switch.
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88 BMW 325is 200K+ SOLD
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Old 11-12-2014, 06:12 AM
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Warm day so did more debugging. To recap. Starter cranks when key turned but keeps cranking even with key removed. Requires you pull the +ve off the battery to stop it. Pulling the yellow wire off the starter and just jumping it and the starter works fine. Also bench tested ok.

Have disconnected the following, all without any change in the situation. That is, any jumping with the yellow wire attached to the starter causes run-on for the starter.

14 pin connector at rear right unplugged
Under seat plug for fuel enrichment pulled off
14 pin at firewall pulled
Every relay next to fuse panel pulled
Yellow wire from engine temp sensor pulled

When I disconnected the yellow wire at the starter and just jumped the starter to fire the engine, I noticed that the alternator light was on at the dash. I had the regulators replaced at the same time as the main engine harness. Could a faulty alternator be causing all this grief somehow?
Old 11-24-2014, 02:56 PM
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In the under dash area on the drivers side accessible from the trunk there should be a single plug for the large gauge yellow wire heading back to the rear of the car.
Find it, disconnect it, and take a voltage reading on the wire coming from the dash area plug. If there is 12 volts on it when the key is in the run position or off your ignition switch is stuck.
Old 11-24-2014, 03:04 PM
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14 pin connector at the rear RIGHT??

if he unplugged the 14 pin connector at the left rear relay panel and it still does the same thing, nothing from there to the front of the car matters.

try removing the power wire from the starter to the alt.
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Old 11-25-2014, 10:02 AM
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Duh. Slight dyslexia. LEFT rear. Not Right.

And yes, once the front plug disconnected and the left rear, nothing else in the front should matter

Previously unplugged the ignition switched and jumped from the to eliminate the mechanical switch. Still runs on.

Three remaining options I think.

1) my wiring diagram shows that the yellow wire from the starter goes to the left rear 14 pin connector and meets another yellow wire from the front that routes through the 14 pin connector next to the firewall. If these two 14 pin connectors are unplugged I should have nothing hanging off the yellow wire that would keep providing 12v to the starter. I suspect a relay failure cause once power applied, removing it still runs the motor but for the life of me can't find such a beast in this part of the circuit. Maybe the diagram is not correct although it's labelled 88911

2). The guy who made the new harness made a mistake

3). Something else I haven't thought of

Stumped actually!!
Old 11-25-2014, 10:14 AM
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Will try d/c alternator wire next. Thx

Old 11-25-2014, 10:15 AM
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