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Old 06-02-2009, 09:57 AM   #1
zedfez
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Unloader Relay Issues

I just swapped the starter on my '88 iX, and now the K5 and K7 unloader relays are not engaging when I turn the car on. With the car off, pin 30 is hot. With the car on, pins 30, 85, and 86 are hot. If I jumper pin 30 to pin 87, the windows and blower work, so I am sure that the problem is in the power box. I have switched the actual relays, so I know that is not the problem.

I have been told that there is a wire on the starter that I may have missed, but as far as I can see they are all connected. Any more guidance on connections to check (and their specific locations) or how the relay pins should test out would be appreciated.
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Old 06-02-2009, 10:18 AM   #2
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Had the same issue it turned out it was the rebuilt starter for me.
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Old 06-02-2009, 10:59 AM   #3
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Did the replacement starter have three connection posts (one large and two small)?

Could it be that the start connections aren't right? There should four wires running to the starter. The larger two of those go on the main power lug, a smaller wire goes to the solenoid lug, and another to the unloader lug.
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Old 06-02-2009, 11:59 AM   #4
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The starter solenoid does have 3 posts. There are 4 wires, 2 with the large ends, on the main lug, one with a medium sized end connected to the bottom lug (I believe that this is the wire from the ignition switch), and one with a small end connected to the top lug. I checked, and this is the wire that goes to the relays. I tested it, and there is a good connection from the terminal on the starter to pin 86 on the relay.

Does this mean that the problem is in the starter solenoid itself?
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Old 06-02-2009, 03:16 PM   #5
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Yup. Wrong kind of starter solenoid. Solution is to move both small wires on the bottom post. (or get a different solenoid)
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Old 06-02-2009, 03:49 PM   #6
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Quote:
Originally Posted by zedfez View Post
The starter solenoid does have 3 posts. There are 4 wires, 2 with the large ends, on the main lug, one with a medium sized end connected to the bottom lug (I believe that this is the wire from the ignition switch), and one with a small end connected to the top lug. I checked, and this is the wire that goes to the relays. I tested it, and there is a good connection from the terminal on the starter to pin 86 on the relay.

Does this mean that the problem is in the starter solenoid itself?
Yes.
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Old 06-03-2009, 09:18 AM   #7
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I tested the top post on the solenoid, and it is hot (12v) when the key is turned to "run". I may be mistaken, but I believe that is what is is supposed to do. This means that when the key is at "run", pin 85 on the relay is hot. Based on my understanding of how the relays work, pin 85 and 87 are for the coil, meaning that if 85 is hot, 87 should provide the ground to complete the circuit through the coil, causing the relay to activate and connecting pin 30 to pin 86. However, with the key at "run" both pins 85 and 87 are hot. I could be mistaken, but this seems wrong to me.

I guess I have two specific questions:
Should the top terminal on the solenoid be hot when the key is at "run"?
Should pin 87 be hot?

As a follow up to the second question, if pin 87 should not be hot, where is the connector that leads to it? I have been going over the wiring diagrams, and it should be connector C114, but I cannot locate that connector.

I know this is really long, and I hope that I am not just beating a dead horse, but I really want to figure out exactly how this system should be working before I go and replace the starter again.
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Old 06-03-2009, 09:42 PM   #8
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I wouldnt replace the starter, I'd move the wire to the other terminal.

Relay terminals 30 and 87 are switch terminals, and 85 and 86 are coil terminals. The locations of the terminals themselves on the relay is non-standard. (thank you BMW...)

Switch terminal 30 is connected to battery positive via (IIRC) C100 which is a lug inside the fusebox. Always hot.

Switch terminal 87 goes to all of your stuff that doesn't work, namely windows, aux fan, blower motor, seat heater, etc.

Coil terminal 86 is connected to the ignition switch, and receives positive voltage any time the key is on run/start.

Coil terminal 85 runs to the starter through C101.

Ok, 86, 87, and 30 are straightforward enough I believe, let me explain what is supposed to happen with 85.

The two relays terminal 85 are wired in parallel, run through the engine harness, then through the starter solenoid windings to ground. With the key in the run position, terminal 86 supplies power to one side of the coil, and the starter solenoid windings provide the ground through terminal 85, engaging both relays. This works because the resistance of the relays is high enough that they do not flow enough current to come close to engaging the starter solenoid.

When starting, the connection to the windings supplies positive voltage to terminal 85, resulting in a voltage difference of 0v across the relay due to terminal 86 still being connected to power via the ignition switch. This causes both relays to disengage, removing power from the various high current draw accessories in the car.

Your issue is essentially an open connection at the starter solenoid. You are measuring the positive voltage through the relays. If you were to ground that wire, you would lose the unloader function, but the accessories would still be ignition controlled via terminal 86.

What happened is, back in the days of carburetors and distributors and other scary things like that, some cars used either a ballast resistor, or resistor wire to drop battery voltage going to the coil so you didn't cook your points and/or fry your transistorized ignition amplifier (cutting edge!)

Voltage drop during cranking became an issue however, so starter solenoids began incorporating another terminal which was just another contact that the starter solenoid disk connected during cranking, connecting both large terminals and the new small terminal on the solenoid together. This small lug was run to the coil in parallel with the resistor wire which was run through the ignition switch like usual, to provide full battery voltage during cranking only. Any other time that terminal was an open circuit so the ignition circuit could do its thing.

OK, fair enough. The point? BMW's fourth terminal doesn't work that way. As it is from the factory in the cars with 4 terminal starters, the fourth terminal connects to the motor terminal, the big one opposite the battery cable connection. This provides the ground/positive signal used to drive the unloader relays like I mentioned before, just using the motor windings as a ground path versus the solenoid windings. Small taillight E30s used three terminal starters, and there was a factory splice to the starter solenoid wire from the unloader wire somewhere in the vicinity of the fusebox. You would essentally be converting your car to the early style unloader circuit by running your unloader wire to the starter solenoid lug.

All that said, many people just ground the damn thing and resist the urge to crank the car while rolling down the windows with a low battery. Either scenario works. Or you could change starters to one with the fourth lug labeled "30h".
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Old 06-04-2009, 06:24 PM   #9
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Thanks for the explanation, I don't think I ever would have figured out how that circuit worked on my own. Nothing frustrates me more than fixing a problem without understanding what I have done.

I ended up just grounding the wire, instead of connecting it to the ignition terminal, because the connector was too small for the post. It's not ideal, but I don't think I have ever tried to use the windows while cranking the starter, so it shouldn't be problematic.
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Old 10-30-2009, 10:03 PM   #10
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Dave, I'd like to say thanks as well - for always re-explaining this issue... if replacing a starter and double checking the unloader relays based on aftermarket rebuilt (autozone) starters is NOT a STICKY... then it should be...

i'll finally have heat again!
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Old 11-11-2009, 08:40 PM   #11
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Damn...

what is it with rebuilt starters and the unloader??

I just replaced my starter with a rebuild unit from NAPA. While the mechanical functions of the starter are perfect and I'm thrilled with the way it cranks, the unloader terminal doesn't provide a ground!

I've permanently grounded pins 85 because I just don't have the motivation to do another starter swap.

Only thing I'm afraid of is, why isn't the starter providing a ground/power? If it ever decides to provide power it will have an easy path to ground.

(maybe I should disconnect that lug from the starter??)
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Old 03-11-2010, 11:44 PM   #12
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Now I've got my rebuilt starter in my hands (a solenoid without a terminal post specifically for the unloader relay wire) and am facing the problem discussed in this thread, it seems like there is a very simple solution to achieving the correct electrical connections. Just attach the unloader relay wire to the second large terminal lug that has the starter motor wire attached to it (the large terminal closest to the motor housing, the one with the wide braid wire attached). The wire lug doesn't fit, but crimping a larger one on is no big deal, or you could make an adapter. Either way, how come nobody has suggested this?
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Old 03-12-2010, 01:03 AM   #13
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My recollection of the wiring diagrams is that the unloader terminal on the starter grounds the unloader relays when the starter isn't engaged. Thus a three terminal starter used on a 9/87 or later car would need that wire grounded. The unloader function would be defeated, but the windows and HVAC would work.
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Old 03-15-2010, 01:10 PM   #14
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The third post on the starter solenoid grounds the unloader relays, causing them to open and remove power from all the accessories while the starter runs. You could easily ground said third wire, and just live with everything having power while the car starts.
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Old 03-22-2010, 07:15 AM   #15
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I've got an '89 325i sedan that I just swapped out the starter. I had an older starter in there before and got a smaller one. I don't have window or hvac power now and after searching found lots about the unloader relay and that I just needed to move the 2 small wires to the bottom post. However I only have the 2 large wires and a black/yellow wire on the bottom post. My last starter had a wire running straight to the engine block, but I think I would be retarded to hookup that with the bottom wire. I have another post on top that is directly linked to the ribbon cable that connects to the solenoid to the main starter housing. I tried hooking up the ground to that, but as I assumed it made no difference.

I'm looking for two things: 1-Any ideas people have. 2-which relay is the unloader relay I need to check. I've worked in car electronics for 5 and a half years now, so relays and troubleshooting don't scare me as long as I know where to look. I thought this relay was amongst the 3 lined up together on the drivers side in the engine bay, but they seemed to check out.
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