Ignition warning light stays on

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taffe9

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Hi, hope someone can help? Warning light stays on & flickers a little when engine speed increased. Battery getting 16.5v across terminals with engine on. Bad earth????
Have added some recent pics. of the car which has covered 49000 miles and has full BMWSH from supplying dealership.
 

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16.5v is much too high. You run the risk of frying the ecu, particularly if there are voltage spikes
Check the external voltage regulator first. Then check and clean all relevant earths.
 
Agree with Simufly - you electronic tachometer and other components will soon be ruined by the excessive voltage. Don't continue driving the car until you get this resolved. Probably it is the external voltage regulator.
 
Agree with voltage regulator being the issue. I went with an internally regulated alternator, yet keep the external regulator just for looks.

My issue was a failing alternator and the car running on battery.
 
From your description, you have more than one problem. The warning light gets power from the battery, which is grounded at the alternator (or voltage regulator in your car) when the car is not running. When the car is started, the voltage produced by the alternator cancels out the battery voltage and the light goes out. If the alternator is putting out less voltage than the battery, the light will come on dimly. If the alternator fails, the light will come on and stay on.

If you are reading more voltage from the alternator than the battery holds, the warning light should not illuminate. Unless there is a lot of resistance in the line from the voltage regulator to the light, in which case the voltage at the light would be less than the battery voltage, causing it to light up.

I had this happen when an old solder joint in the wire from my alternator to the warning light corroded with age. The corrosion increased the resistance in the line, causing the light to illuminate and causing a faulty low voltage reading to the alternator. Reading this low voltage, the alternator put out more voltage to charge the system; in my case it went to more than 19 volts.

Check the resistance on the line running from the voltage regulator to the "ignition light." Resistance in this wire will trick your alternator into putting out too much voltage. This condition fried my voltage regulator and a battery.
 
Ohmess said:
..

If you are reading more voltage from the alternator than the battery holds, the warning light should not illuminate...
Click to expand...

I am not sure I agree with that, if the voltage regulator is broken and the alternator puts a higher voltage than the battery then the light would illuminate by virtue of the current going into the battery through the warning light. Unless there is a diode in that circuit.

Agree on not driving the car until the voltage regulation is solved like Jay suggests.
 
More Info.

Thanks for all your help, have now had a little time to fiddle around and test a few ideas; jumped the blue D+/61 wire to the black DF wire on the voltage regulator started the car and the ignition light glowed even brighter. Checked the resistance of the blue wire from the back of the alternator to the connector block under the instrument pod and this reads 0.04 ohms. So I guess its time to take the alternator out & overhaul it?
 
taffe9 said:
So I guess its time to take the alternator out & overhaul it?
Click to expand...

Yes, but bring the regulator along too when you visit your local alternator rebuild shop.

It is always useful to include your city & state in messages, so that others can suggest shops in your area. Automotive electrical shops are becoming scarce - perhaps you know of a good one in your locale, but if not, someone else might.
 
Location

Thanks for the advice. Have updated my profile, am based in Wildest West Wales quite close to Ireland. Have ordered the parts to rebuild the alternator & thought I'd put it together myself......how wrong can it go??????????
 
Sorted

Thanks for all your help guys, finally found the time to get the alternator out, v. tricky without removing anything else. Replaced the Diode Pack & Brushes (for good measure, whist I was there), total cost £22.30 from Jaymic. All looks good now, ignition light comes on & goes off as it should. When I tested the alternator output ( with an old lucas ammeter ) there was none so maybe too many volts & no amps??????
 
If you are hooked up properly and the warning light goes out after starting the car, you should get a voltage measurement.

Can you describe the test you conducted?
 
Test

Hi, as my multi-meter can only handle 30amps (I must get a new one) I used an old ammeter that I new was good. I had removed from one of my others as it was not the right period. Anyway disconnected the B+ cable (red) from the back of the alternator and connected the ammeter in series between the B+ and the battery positive. I did all this with the earth disconnected & engine off. Reconnected the earth, switched on and run the engine at 2500rpm long enough to establish no readin on the ammeter. Hope this helps?
 
Hmmm. That seems odd. Conduct that same test, but switch your meter to DC volts. Should be around 13.9 or so.
 
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