Not sure which thread it was in but basically the B+ jump terminal under the hood was getting hot and was very corroded. The owner repalced the jump terminal with a new one, cleaned all the contacts and issue was solved.

It was also determined that on some cars the B+ from that battery actually connects to the alternator and the starter via this jump terminal, so it's electrical condition matters a lot.

Remeber to disconnect the battery B+ BEFORE goofing with the B+ jump terminal - or welding happens. :yikes:

Found it...

https://xoutpost.com/bmw-sav-forums/...ch-solved.html

Thanks much. My jumping B+ is connected to the alternator for sure cause it's getting alternator voltage, but I'm not sure if the battery cable is connected to the alternator via the jumping terminal. I'll do the jumping cable test first before anything else.

Another test you could try is a voltage drop test while cranking...

Using a multimeter, set to 20 volt range, connect the negaitve (black) lead to the B+ jump terminal and the positive lead (red) to the B+ battery terminal. Use any long wire to extend one of the leads - this wire wil carry almost zero current so it doesn't need to be a big wire.

Inital reading should be close to zero volts. Now crank the car and read the voltage that appears of the meter while cranking. Anything more than a volt or two indicates that the wiring from the battery to the jump terminal is faulty somewhere.

Good news! I did the jumping cable test and it fired right up, alternator is also charging the battery. so we can be confident now that the issue is narrowed down some where on the battery cable?

Great news! :thumbup:

Looking at this diagram there's not much left to check..

http://www.bimmerboard.com/members/q...%20Diagram.jpg

You're looking for any joint in the line from the battery B+ to the jump terminal. The BST is still the most likely culprit....

Awesome diagram, exactly the same layout as my car. I'll check everything tomorrow when there's light. Thanks!

The problem was discovered in the other thread because the B+ terminal got HOT from high resistance. There could also be a high resistance issue at the BST. Or just at the battery terminal itself classic post corrosion.


Sent from my iPhone using Tapatalk Pro

Thanks so much for everyone's help. The issue is now resolved. It was indeed a bad connection on the B+ jumping terminal under the hood, the nut was very loose.
After a new battery and a starter I learned my lessons now to always diagnos the "small" things first.
Thanks again everyone!

Hooray! Glad it's sorted... :thumbup: