Where is this thick/big red cable (with a brass loop at its end) connected to? - Bimmerfest - BMW Forums

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E30 (1982 - 1993)
God's Chariot. The E30 was produced primarily from 1982 through 1991. The cabriolet was the one exception which was produced through 1993.

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Old 09-10-2019, 06:38 PM
Learning Learning is offline
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Mein Auto: 1991 BMW 318i
Where is this thick/big red cable (with a brass loop at its end) connected to?

Good day, everyone,

I have a 1991 BMW 318i 4 cylinder 1.8L 4-door E30 M42 sedan.

Few days ago, I was driving and suddenly my car was hesitating on the road and the check engine light came on. I drove for few minutes to a safe spot to park and called AAA to tow it to my house. I did a stomp test and the code was 1231 which is "Battery Voltage / DME Main Relay error code can mean that battery voltage is out of range (either too high or too low), or that battery was disconnected. Test charging system and /or battery to find problem cause."
About a year ago, I had the same problem and a mechanic changed the Voltage Regulator and it worked!
From watching YouTube videos, I learned that most likely it was the same problem again and so I easily changed the VR myself, then warmed it up nicely for about 10 minutes (thinking that I solved the problem), yet, after test driving my car for about 1 minute, it hesitated again, the check engine light came on, and the car stopped. I called AAA battery service and the AAA guy said knew about BMW E30 because he's had several and worked on them through out the years.
We opened the hood, the guy looked into the engine, and he said to have found the problem which was a BIG/THICK/FAT RED WIRE/CABLE THAT WAS JUST HANGING FREELY BELOW/UNDER THE ALTERNATOR. It had a BRASS/BROWN looking metal loop at its end with only half of the metal loop remaining. Half of it has broken off. He said happily. "I found the problem!". He also said that this THICK RED CABLE should be connected to the B+ TERMINAL of the alternator. The question: was he correct? I just wanted to confirm with the experts here.
Where is the B+ TERMINAL of the alternator?
Hopefully, someone can help explaining.

Upon checking closely, I found this thick cable has too big of a metal loop for any of the studs/connections on the back of the alternator to accommodate.
I don't want to attach this thick red wire to the wrong terminal/part of the car/alternator. I believe this is just a very simple problem, but I don't know much about car. I believe someone here can help.
Thanks so much in advance for you answers.

PS: Could this big red cable be "Engine to Chassis Ground Cable". I just remembered about 10 years ago my car was hesitating with check engine light on for many weeks and finally found it was the Engine to Chassis Ground Cable that went bad (but not detached). The plastic/rubber insulator was all gone/ripped exposing the bare wire.
Does the alternator of this type of BMW have to have a ground wire?

I've attached pictures below. As you can see, the cable is just hanging lose below with its broken metal loop. I pulled it up to take pictures of it to show it close up.
The middle top part of the 4th picture shows the other end of this cable underneath the car which goes/attaches somewhere in the middle underneath the car.

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Last edited by Learning; 09-11-2019 at 12:02 PM.
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Old 09-14-2019, 08:50 PM
hornhospital's Avatar
hornhospital hornhospital is offline
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Get a mirror and see of there is one or two small wires and one large one connected to the alternator. Each should be retained by a nut, the small ones on the small stud(s), and a large one on the large stud. IF the large wire is missing from the alternator, you've found where that wire goes. It looks like the connector was loose for some time, and was a high resistance joint, resulting it parting and falling off. If the remaining part of the connector were closed back to a circle it wouldn't be too big for the stud.

If there still is a large wire to the large stud on the alternator, all bets are off.

With that said, DO NOT reconnect it to the alternator until you confirm it goes to the main 12 volt buss/jump post on the firewall. There should be three heavy wires there. One from the battery in the trunk, one going from there to the starter, and one to the alternator.
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