Need help diagnosing electrical problem

My 88 325ic stopped running in mid-stride a couple of days ago: we were almost done with a 30-minute run back home in the foothills west of Denver when the dash lit up with warning lights and the engine quit. I got her towed home and have spent a couple of days looking for the problem without much success.
What I've learned: all the auxiliary gear is working (lights, wipers, radio, fuel pump, etc.) except the power windows, and the idle air solenoid doesn't purr when the ignition is On. (The fuel pump works only when jumped directly to the battery; connecting the 30 and 87 terminals at the relay doesn't do anything, and the pump doesn't come on when the starter is engaged.)
I've replaced the main relay with a spare, to no effect.
The absence of a hum and vibration from the idle air solenoid indicates to me that this is an electrical problem further upstream (failure of the IAS wouldn't have made the engine quit in mid-run), but I'm unsure about how to diagnose the problem further. I have a spare ECU, but I've got some reservations about subbing it in, because of the possibility that there's a short in the system.
Any advice or suggestions will be greatly appreciated,guys.

Originally Posted by Dandy dog

My 88 325ic stopped running in mid-stride a couple of days ago: we were almost done with a 30-minute run back home in the foothills west of Denver when the dash lit up with warning lights and the engine quit. I got her towed home and have spent a couple of days looking for the problem without much success.
What I've learned: all the auxiliary gear is working (lights, wipers, radio, fuel pump, etc.) except the power windows, and the idle air solenoid doesn't purr when the ignition is On. (The fuel pump works only when jumped directly to the battery; connecting the 30 and 87 terminals at the relay doesn't do anything, and the pump doesn't come on when the starter is engaged.)
I've replaced the main relay with a spare, to no effect.
The absence of a hum and vibration from the idle air solenoid indicates to me that this is an electrical problem further upstream (failure of the IAS wouldn't have made the engine quit in mid-run), but I'm unsure about how to diagnose the problem further. I have a spare ECU, but I've got some reservations about subbing it in, because of the possibility that there's a short in the system.
Any advice or suggestions will be greatly appreciated,guys.

If you have the battery located in the trunk, the thinner black wire that runs forward to the engine bay has a fusable link inbedded in it and this is the wire that serves the engine functions.

Measure this wire to check if the fusable link has blown.

Fuses my car died mid romp turned out to be a fuse

Wicked Fast Entertainment

No easy one -Keep testing with volt meter and test lamp. As a starting point, do you have power in and out of the ign switch?

No ICV.
Disconnect plug C191 or whatever the engine loom plug is. It is located just below the throttle-body.
Clean the contacts, and pull the boot off of the engine loom side to see if there is corrosion or contamination.
No Main Relay.
The lack of switching voltage at the main relay suggests that your ignition switch may have failed. Look for exiting voltage as per previous poster's suggestion.
Test for continuity on the DME power cable.

No Power windows.
The unloader relay may also need to be tested or the power window circuit breaker(if applicable) may have been tripped.


m

Update:
Responses in order of appearance:
Bill: The battery is in the engine compartment.
Wicked fast: which fuse?
BMWDad: I've got current to all the warning lights when I turn the ignition On, and to the radio, wipers, etc.
7pilot: Yeah, I've heard about the C191, but I've never had any problems with mine. (I'll check, though.)

Results from this morning's testing:
1) There IS current at fuse 17, so the windows may be a separate problem. (I've had trouble with them previously.)
2) However, there is NO voltage at the center contact of the ICS connector. I'll check continuity to the DME.
What do you guys think about sending in my second-string DME.?
Thanks for your help, guys.

With the DME connected:
I've got battery voltage at terminal 30 of the fuel pump relay.
I've got battery voltage at terminals 30 and 86 of the main relay.
I've got NO voltage at the center terminal of the idle air stabilizer.
With the DME disconnected,
The main relay clicks when terminal 36 of the DME connector is grounded.
With 36 and 2 jumped, there's battery voltage at 37 and 18.
With 36 and 2 jumped, there's battery voltage at the center terminal of the IAS.
With 36 and 2 jumped, the fuel pump runs when 3 is grounded.
With 36 and 2 jumped, the injectors click open when 16 or 17 is grounded.

All of which looks totally normal to me (except, of course, for the IAS reading.) anybody see anything I'm missing?

I'm gonna send in the back-up DME.

Rats. Nothing.

For the time being, I'm out of ideas. If anybody's got any suggestions, I'll be glad to follow up on them tomorrow.
Neil

sounds like the alternator has failed and the battery has run out of charge to me, but i didnt read ALL of the posts above

From memory all '30' terminals have battery voltage on them all the time. The control system (there are several) will pull in the relay to energise whatever may be on the end of the output wire - ie fuel pump.

Fuse 12 but i realized yours is an 88 ic mines an 89 325i and they changed quite a lot of stuff in there cars after 11/88

Wicked Fast Entertainment

May I have the envelope, please ? . . .
And the (probable) winners are . . . BMWFatherFigure and 7pilot!
(It looks like I'm not getting current out of the ignition switch main lead.)
Thanks, guys - I'll confirm the diagnosis in the morning and post something for the archives.
Neil

Not that simple: turns out I've got current in and out of the ignition switch at the c200, but not at another (smaller) green wire under the dash on the driver' side (possibly c209?)
The 2.5 green wire out of c200 disappears into the harness almost immediately. Does anyone know where the next connector downstream is? Or have a wiring diagram that he can send me a link to?
Thanks -
Neil

Assuming that the basic flow is battery>ignition switch>relays>fuses, the next stop for that 2.5 green wire ought to be the relays.
I've got battery voltage at terminals 30 and 86 of the main, with the ignition On and Off; I have voltage at 30 of the K5 relay with the ignition Off, and at both 30 and 86 of K5 when the ignition is On.
Come to think of it, I've also got battery voltage at fuse 17 (from an earlier test.)
Some of my assumptions have GOT to be wrong.
I really need a wiring diagram.

Originally Posted by Dandy dog

I really need a wiring diagram.

Right-click on this and "save as":

http://wedophones.com/Manuals/BMW/19...g%20Manual.pdf

That's the BMW Electrical Troubleshooting Manual for your car.

Thanks, HHS - That's an enormous help.

The problems with the windows and the detector come from the same place: There's a green wire under the driver's side of the dash that used to be hot, but isn't any more.
The wire that's supposed to provide current to both the windows and the detector comes out of a connector that I believe to be C208 (I haven't been able to confirm this because I can't find C208 on any of the wiring diagrams hh sent me. (it's in the "Connector Locations" pictures and in the "Component List" section, but I haven't been able to locate it on any of the diagrams.)
The connector in question has two wires, both green and probably .5 or 1, on one side, and two on the other, one green and one green and red. The latter green wire used to be hot when the ignition is On, but now shows no voltage; the red and green wire, however, is switched Hot.
It's possible that these wires are associated in some way with the Power Window Circuit Breaker that appears on the wiring diagrams (but not on my car: there's a factory filler piece on the dash where the breaker should be.)
Does this speak to anyone? Has anybody ever seen C208 on a wiring diagram?
In a related development, I found that the voltage at terminal 87 of the main relay is only 2.25 volts with the ignition On. This does NOT seem right, and probably accounts for the fact that the IAS isn't buzzing. (Tapping the center terminal of the IAS to 30 or 86 of the main relay should confirm that the IAS is working, right?)
So: I haven't found the source of the problem, but I think I'm narrowing things down.
Any ideas, suggestions or comments?
Thanks again, guys -
Neil
(Edit) Wait a minute: That was a reading of 2.25 volts at terminal 87 of the main relay SOCKET, with the relay itself removed. 87 should get its voltage from the other side of the relay; there shouldn't be any reading at all without the relay in place.