I have an '85 740 turbo diesel with 57k miles (yes, 57k) and the other day my battery went dead. I had to have it jumped twice, then I took it to a shop where i had the alternator replaced. The car died again today so I just replaced the battery. When I turn the car off the batter light comes on. Any ideas what might be the problem? When I look in the engine bay at the alternator, it looks like there are two plugs that are supposed to be connected, but they arent. Dont know if that has anything to do with it.

 

Just a good test to perform here is to remove the negative battery terminal and run a test light between the negative terminal and the negative battery post with the key off. If the test light is on start removing fuses one at a time until the light goes out then you know what is draining the battery. On a side note you maight want to replace the ignition switch as that is the only time I have seen the battery light stay on after the switch is turned off. Hope that at least gives you a place to start looking.

 

I actually agree with the bad ignition switch point; if the alt light goes out when the car's running but stays on with ignition off, then it's likely is bad ignition switch.

Might try jiggling the key around near the off position and see if you can get the alt light to go off; if so, that's it for sure.

Those disconnected wires sound concerning also; post a pic to show us what you're talking about.

 

The most logical place to look for a failure that has happened after service work is the service work.
Check teh alternator wiring is correctly hooked up before you go further.

Regards, Andrew.