Subject: That is a good list. Here are a few technicalities> Author: kff (moderator) : member since February, 2004 : 4035 posts Posted on: 2005-03-08 11:47:27

The alterntor needs an exciter voltage to start charging and as you say the loss of the dash light (burned out or broken filament) so electricity does not flow through it will prevent this exciter voltage from reaching the alternator. BMW figured this out and added a resistor across the light bulb in later dash clusters, but I don't know the year of these changes for the different cars. So to verify the lamp works, check that it comes on when the key is in the position before start on startup and the dash lights come on.

The door lock heater for the driver's door is activated by lifting the driver's door handle. There is a metal flap on a circuit board that touches ground when the handle is lifted. The heater can go bad so it the door lock is hot the heater circuit is not right. This circuit also activates the interior light delay circuit allowing the interior laights to stay on 7 seconds after the last door is closed, unless the key is turned in the ignition. This light control relay can fail and drain power from the battery, too.

It was hinted at that the trunk light can also drain a battery.

The use of an ammeter in the circuit is the way to tell where the problem lies. It can be done at the battery, but if no results are the answer, reconnect the battery and use the meter at each fuse. Remove the fuse and check the amp draw across the fuse connections. None should be above 25 millliamps or so. If you find a high one, determine the circuits on that fuse and narrow down the search. That s as far I I can go.

• Mystery Battery drain compiled info - Martin 2005-01-13 21:46:01 (16788 views)
  • That is a good list. Here are a few technicalities> - kff 2005-03-08 11:47:27 (2630 views)
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