850ci dead on arrival

I have a 1993 BMW 850ci with 170,000 miles. Family owned since new. Today it did something entirely odd. My wife was driving it in the driveway, and it completely died, all dials went to black. There is not so much as a map light that works. Door locks are dead. There's absolutely no electric whatsoever. I just replaced the main battery. The other is maybe five years old. I tried to jump start it and still nothing. Help!

Hmm, the only other thing that I can think of is the alternator.

When you connected the battery, did you see any sparks coming from the battery terminals ?
It might be an indicator that a power line is shorted.
Also make sure that you have good ground, try and connect a wire from the negative terminal of the battery to the body directly, but make sure it's the negative pole.

It would be good to check the voltage at the alternator to see if the power gets there.

There was no spark when I detached the new battery.

First thing is to get another new battery to match the one you just put in. The old one will kill the new one fairly quickly.

In the line in front of the passenger side battery is a fusible link (lump in the cable). They never blow out but they sometimes break when the battery is changed. Some time it waits a week or more to actually separate.

check the important grounds on the engine and body. Sometimes they may look good but are corroded where they touch the body or engine.

Thanks for the advice. I'll look into it and report back.

Yeah, check the volts on the battery - Jump start it and see if it even starts... Sounds like alternator.

No offense meant to any on this board but the alternator going out would not cause all the lights to go out. The battery would drain if it were out but it would start running pretty bad before it died and the lights would still come on faintly. The first thing that popped into my head was a fuseable link as stated by TerryY. Good luck!

I got the car started. I jiggled the passenger side positive battery cables and then the lights started coming on. But I'm sure not what the heck the problem is. I'm going to clean up all the connections and get a volt meter on there. However, there doesn't seem to be much corrosion. Any other ideas?

Tighten your battery cables correctly

do a voltage drop test to verify the condition of the circuit(s). a poor connection may not be readily visible, but voltage drop tests are the best way to look for these sorts of issues. i added the link as it does a better job of 'splainin what the heck a voltage drop test is (unless you are an electrical engeneer, in which case please accept my appology...).

i hope this helps.

http://www.engine-light-help.com/voltage-drop.html

df

Why are you guys overcomplicating this??

You wiggled the battery cable, that means its loose, so get out there an tighten it up.... no need to read a electrical engeneering manual to figure this one out.

not to split hairs, as you are correct about making certain the connections are tight. however, according to the op, he tried to jump the vehicle without avail. i have jumped vehicles that didn't have a battery in them, which would indicate to me one of two things.

1-the jumper unit (battery or charge pak) was too low to even turn the lights on, or

2-there was (is??) a break in the wire somewhere (see the post from terry). since one cannot see through the insulation, and the op asked for advice on 'how to' for repairs i figured that i would add a link to a very easy to do (yet very often overlooked, even by ase master techs) diagnostic test to check the fusible link as well as the rest of the cable.

since i am not able to be there, i try to cover the basics (unless one has already done so), ask some questions, and try to give advice on what information i have gathered. i have to assume that one asking questions is willing to attempt reasonable repairs, and able to realize when he/she does not posess the necessary skill to perform the task they are asking advice about and seek professional assistance.


df+

As a followup one year later: I think it was the battery cable...I tightened it up and haven't had the same problem since.

Glad to hear that. You do know by now that the 8 series have 2 batteries, and that they must be identical, and replaced TOGETHER. If you choose to just do 1, then you are just prematurely killing the new one. These cars need ALOT of juice for all the modules and other electronic goodies, and if the batteries are not totally healthy, you WILL have electrical gremlins.

I believe I've been replacing them together. No electrical demons otherwise. Thanks for the tip!