740 Warning Lights stay on

TommyB · Post by **TommyB** » 21 Nov 2009, 06:37

My 740 non-turbo sedan with 200K miles is still a very nice ride and runs great. But out of the blue, all the dash warning lights have decided to just stay on. I start up the car and the lights won't go off. This did happen after a driving rain, but I am not sure that had anything to do with it. Where should I start looking? Thanks.

Post by **billofdurham** » 21 Nov 2009, 10:34

This is often an indication that the alternator isn't working as it should.

Check the drive belt for correct tension. Check the connections at the alternator for tightness and check the wiring at the alternator for defects in the insulation.

With a voltmeter check the battery with all lights etc switched off. It should read about 12 volts.

Now test the alternator:
1) Start the car and run at a normal idle.

2) Turn on headlights to main beam.

3) Connect the voltmeter directly across the battery terminals.

4) The battery voltage should read between 13.5 and 14.5 volts. If it is lower than 14.2 volts the alternator probably has one or more bad diodes and needs replacing or rebuilding.

5) Increase engine speed to about 1500rpm. The battery voltage should now read between 14.2 and 14.6 volts.

6) Maintain the 1500rpm and turn off the headlights. Run this test for about a minute. The battery voltage should never exceed 14.8 Volts. If it does, the voltage regulator is probably faulty and over charging the battery.

Bill.

TommyB · Post by **TommyB** » 25 Nov 2009, 06:47

Bill,

Thanks for the direction. A new set of brushes and we are back in action.

Tommyb

Post by **billofdurham** » 25 Nov 2009, 11:44

Thank you for the update.

Bill.