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Thread: Dead battery, now dead car??
10-13-2010 05:25 PM #1
Dead battery, now dead car??
The wife's '91 325i was dead the other day - like dead, dead. The battery measured like 0.7 volts. When I hooked up the charger I heard a little humming sound that I traced to the power antenna. I disconnected the antenna and left the charger on the battery over night to see if I could revive it, but no luck.
I got a new battery and installed it, but the next morning my wife called and said the car wouldn't start. So here's the situation - the "Brake Lining" light is on ALL THE TIME - even with the key out of the ignition. When you turn the key on the other lights come on, the chime sounds, the tach needle moves a bit, but nothing whatsoever happens when you try to turn it over.
I am thinking something is wacky since the Brake Lining light will not go off without disconnecting the battery, but even if something is fried, I thought the start circuit was independent of any computer or cluster goofiness?
10-13-2010 09:12 PM #2
OK, so I found some more electrical stuff happening, and I can not quite figure out what is going on. Here it is in a nutshell:
Key off, out of ignition:
- Power antenna constantly running, antenna in down position
- "Brake Lining" light on
- Power windows functional by way of a turned on K5 load reduction relay
- All instrument lights come on, fuel gauge rises, tach needle moves slightly, chime sounds
- Power windows no longer functional
- Did not check the power antenna
- Same as Key On, no turning or clicking of the starter
I checked out the K5 relay for the power windows and the relay tests good. The Bentley manual does not have the wiring diagram information for the K5 relay, or the Brake Lining light, or the power antenna. Ideas?
10-15-2010 08:49 AM #3
That's a tough one
I don't have direct experience, but I'd download the wiring diagram for your car and start tracing the circuits back to a common point.
10-15-2010 02:32 PM #4
10-17-2010 03:38 PM #5
So when an E30 BMW 325i has the positive lead on the starter solenoid short to the load reduction relay control lead, the connection to the load reduction relays that are normally grounded through the starter motor become energized and the other side of the relay coil has a residual path to ground through the ignition circuit, thus powering the circuits controlled by the load reduction relays even when the key is not in the ignition. Said short can also cause enough heat in the new path to ground through the starter motor brushes that the solder connecting the brushes will liquify and and disconnect the brushes from the terminals, and also at some point completely wipe out the battery. Apparently.
10-18-2010 07:45 PM #6
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