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Electrical Problem

Posted: Sun Feb 24, 2019 9:54 pm
by cory58
So I have the first electrical problem with the E12 ('77 530i) and hope the collective wisdom here can help. I've searched the board and can't find a post for the same problem.

My starter got unreliable. It would work fine for a while and then not. The solenoid would click but the starter would not turn the engine. No paperwork of starter ever being replaced (85k orig miles), so I figured it was time and ordered an E34 starter. Installed it, same problem.

Took some readings with a multimeter and tried to troubleshoot per the a factory manual and Haynes manual. Before I could figure anything out, I decided to remove the battery hold-down and move the battery over a little bit, because the main power wire from the battery to starter was stretched a little bit due to the solenoid on the new starter being shorter. After moving the battery over, the new starter worked but the car wouldn't run. It will fire with the starter engaged but will not run at all. This was a new problem.

I then thought to check the fuel pump, so I put the car on the lift, turned the key and the fuel pump was quiet. Started getting ready to check the wiring to the fuel pump then smelled something coming from the engine bay. A wire to the coil was smoking! It was the wire connected to the same small post as the black/red wire to the starter. Per the wiring diagram, it's a "transparent" wire that becomes green and (best I can tell) goes to the 7-wire connector on the side of the fuse box. The wire fried so bad that the the insulation is completely gone for at least 2 feet from the coil.

After letting everything cool down for a few minutes, I turned the key back to "on" and the wire immediately started to heat up again. Unplugging the red/black wire from the starter fixed the hot wire problem. I was able to leave the key in the on position without the wire to the coil overheating.

Sorry for the long set up, so here are the questions.

1. The starter is an updated Bosch OEM for a newer M30, so I'm guessing the connections are the same. With the main battery power post at three o-clock, I connected the red/black wire to the smaller spade terminal at twelve o'clock and connected the black/yellow wire to the larger spade connector at six o'clock. The ground wire from the solenoid to the stater is at nine o'clock. Is this correct?

2. It seems like more than a coincidence that the starter worked and then there was a new electrical problem after I moved the battery over a little bit. I took the battery completely out and glanced at the wiring around the battery. Nothing obviously pinched, worn or grounded out. Any thoughts?

3. Any thoughts on why the wire to the coil would fry when the red/black wire is connected to the starter but not when it's disconnected?

4. Any other thoughts or ideas of what the problem(s) could be? Feel free to ask me questions for diagnosis.

All responses will be greatly appreciated!

Thanks, Cory

Re: Electrical Problem

Posted: Mon Feb 25, 2019 5:45 am
by 528i-1981
Hi Cory - Did you check the ballast resistors between the ECU and the starter and in the black/red circuit before the coil? You can do this without energizing the circuit. The green wire goes to the ECU so if the resistors check out, the ECU could be the next place to check if you can swap another one in.

Re: Electrical Problem

Posted: Tue Feb 26, 2019 1:39 am
by Lock
We don't have any kind of auto priming with our fuel pumps, they only turn on when the AFM door flap moves due to airflow so the pump won't operate unless you take the rubber boot off and push the flap (I slide a long screwdriver in there and poke it when I need to). I put in a 2-second relay timer on mine to make cold starting better. But I don't think that's the issue.

It sounds like currently that burnt wire is being grounded at the starter end. Do you have an auto? I know that the auto trans dipstick tube gets very close to the lines (I've hit that tube on the starter main line before - not pretty). I unfortunately don't know the correct line outs on the starter, but it sounds like it's being grounded at/near the starter, power is applied to the coil when the car is set to 'on' and then going via the dropping resistor through that wire and cooking it. The fuse would normally blow but because it's connected via a resistor maybe it's not drawing enough current to blow, but it is enough to heat the wire.

The weird thing is, you said the car starts and fires during starting, but doesn't run. That would normally indicate the coil circuit is failed, so when you're cranking voltage is applied to the coil and it will fire. As soon as you stop cranking, voltage stops and the coil will go dead along with the engine.

So if it were me, I'd temporarily bypass all of that circuit, run a wire (preferably fused) from the battery + terminal direct to the + on the coil (ideally you would unplug the bypass resistor wires and connect it via one of the bypass resistors as it's a 9v coil). If the engine starts and runs, your coil, starter and engine are fine and there's probably a short or two in your wiring. My guess is the short is somewhere between the starter wiring and the fusebox on the 40+ year old wiring.

It may be something else, but when you switch the car to 'on' and that wire burns up, it sounds to me like it's likely the coil power is being earthed through it. Maybe find a pinout of that starter to double-check? I'm not sure the correct layout of the starter and yours might be different.

Re: Electrical Problem

Posted: Tue Feb 26, 2019 7:15 am
by 528i-1981
That sounds right. A failed resistor would mean an open circuit (infinite resistance), so that can’t be it. During start, isn’t the ballast resistor bypassed to get full battery voltage to the coil? This would explain why the car turned over when cranking then dies when the key goes to “on”. This would more clearly implicate the burnt wire .... but you kinda already know that because it’s BURNT. But a short in that wire would mean the reduced voltage with the key in the “on” position was never reaching the coil.

Re: Electrical Problem

Posted: Tue Feb 26, 2019 8:01 pm
by cory58
Thanks for the replies! So I've now learned what a ballast resistor is and what is does. Thanks Google and Hack Mechanic! This is what autoblog lists as the first symptom of a failed ballast resistor:

"The most obvious symptoms will be the vehicle starts, but then immediately dies as soon as you release the key."

Sound familiar? I also agree that a melted wire usually means something is shorted to ground, so I'm wondering if there are two problems. Maybe one was caused by my running the new starter over and over for longer than usual duty cycles.

I have the ignition wiring harness almost completely removed from the car. The outer cover is partially burned through, but I plan to open up most/all of the rest to see if there are any obvious shorts, and then repair it. Running a direct wire from the battery to the resistor or coil is a good idea and I will probably try that as part of the diagnosis.

Regarding the ballast resistor, I searched and searched and cannot find it in the engine compartment. Where should it be on a 530i? I also can't find it anywhere on It's easy to find for a 528i, but the same diagram for the 530i has the ballast resistor greyed out. Strange.

Thanks again!


Re: Electrical Problem

Posted: Tue Feb 26, 2019 8:17 pm
by Dale
Should be mounted to one of the fenders - believe it is the battery side. Looks like two white sausages with wires coming out.

Buffalo, NY

Re: Electrical Problem

Posted: Tue Feb 26, 2019 8:32 pm
by cory58
Thanks Dale. I'll check again. Must be hidden well.

Just found a discussion of ballast resistors on 2002faq, with this: "The Blue coil has an internal resistor, do not use an external resistor with this coil." I wonder if that applies to my car. It has a blue coil.

Also found this: "Make sure you have your bypass wire on the correct terminal on your starter because if you don't it will attempt to backfeed your starter and your resistor will burn up and the wire will get fried." Thought I wired the new starter just like the old one (as described in my original post), but I'll be checking that too.


Re: Electrical Problem

Posted: Sat Apr 20, 2019 7:22 pm
by cory58
I finally had time to repair the wiring harness, so thought I'd close the loop on this thread.

One other loose end - my car definitely doesn't have a ballast resistor, so I guess I have the blue coil with the internal resistance.

In my research, I read on a forum somewhere (maybe 2002faq or mye28) that when upgrading to the E34 starter it may be necessary to not connect the bypass wire to the new starter, so I tried it. Connected the signal wire but left the red/black wire disconnected. At first, I could hear the coil click when I turned the key but the starter wouldn't turn (original problem), but after a few tries the engine turned over and ran. After running it for short periods a few times and checking everything, I took it for a drive and it ran fine.

So, I'm not sure what's different about the E34 starter, but not connecting the red/black wire seems to have solved one problem. I plan to drive the car as much as possible before taking it to The Vintage, to see if I can get comfortable that the original problem (starter not working intermittently) won't strand me.