I change the battery an alternator an the light still stays on
Brother Mark, changing the battery with a new one being done won't make the light go out, as you noticed. Light is still on so you changed the alternator. Good, but the battery light is STILL on. This only means that the charging circuit from the alternator is not working in the voltage regulator or the wiring is not connected properly to the alternator/regulator. A new battery will show over 13 to 13.5 volts not connected. An old battery will still show 12 volts and still be weak or bad. After connected and engine running, the system will show at least 14 volts because alternator/regulator is working properly, using a voltmeter/load tester connected to the battery. If after replacing the battery and alternator it is still reading 12 to 13.5 volts, it is not working and the light will stay lit on the dash. You may have purchased a faulty alternator if the system tests out this way. Have your system checked with a volt meter or load tester bit be sure all the connections are proper and clean.
SOURCE: 2003 bmw 525i
If the brake lights are really on (?) this represents about a 4-5 ampere drain that would drag down most batteries in less than a day. (Could be over 100 ampere/hours.)
I don't know your car but brake lights can be controlled by a switch operated by the pedal suspension or a pressure switch that monitors hydraulic pressure in the braking circuit.
If your brake lights are on, the switch that controls them has failed or a relay that is operated by the switch.
If the car seems sluggish or pulls when driven, it could be a failure in the ABS circuit since that is a high-demand (normally intermittant) load.
The best way to locate the problem would be to monitor the current drain with a meter in series from the battery (engine off, monitor the ground side) and pull and replace fuses one-by-one to see which circuit is the culprit.
SOURCE: alternator for BMW
if the alternator is tested and proved defective then u need a new alternator, years mean nothing, how many miles?
SOURCE: 2003 bmw alternator giving 14volt no charge to battery
Yes it can. But it must be turned on first. -------------------------------------------------------------------------
tacho pro
SOURCE: Have a 2010 Lincoln town car signature but the
check to see if charging voltage is achieved while running..must be close to 14.5..if under 12.6 you are not getting proper charge voltage and the master control module system will shut down if operating voltage drops below 10.5..
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