1986 bmw l7
Hi I have an 86 L7 and have been having some issues. I changed the battery and that solved the issue for about a day. Then I had the alternator tested and it failed. Purchased a new alternator and I am having the same issue. I don't have a fuse diagram so I am not sure which fuse to check for if there is one? Car will not start without a jump and once its jumped it instantly dies once disconnected from the other vehicle. I am new to BMW and am not sure if this is a known issue and couldn't find anything via search.
Thanks for any help or input