Suspected alternator failure but no light on the dash...
Discussion
Battery is not charging in my Saab - load test shows the battery as being OK, but getting very little or no charging effect (shows 12v whilst revving at 2000 RPM).
Textbook alternator failure so far - but no red light on the dash. It comes on with the ignition fine, and I have not change the lamp in it, so it's the correct wattage.
It functioned in the expected way perfectly a couple of years ago when the brushes had worn right down and I had to replace the regulator.
Next step is to change the alternator, but why on earth do I not get a red lamp?
Textbook alternator failure so far - but no red light on the dash. It comes on with the ignition fine, and I have not change the lamp in it, so it's the correct wattage.
It functioned in the expected way perfectly a couple of years ago when the brushes had worn right down and I had to replace the regulator.
Next step is to change the alternator, but why on earth do I not get a red lamp?
If the wire from the light to the alternator is broken then not only will the light not light up the alternator won't start charging the battery either!
Does the light come on and then go out, or just never come on? If it never comes on the wiring is probably broken, or the bulb has blown which has the same effect.
Does the light come on and then go out, or just never come on? If it never comes on the wiring is probably broken, or the bulb has blown which has the same effect.
If you think the alternator wiring is not right a simple way to eliminate that possible problem is to make up a lead with a side lamp (2.5W) bulb in series.
- With ignition off remove the control lead to the alternator (the thinner lead usually on a 1/4" Lucar connector).
- Connect one end of your made up bulb lead to the now empty alternator terminal. Connect the other end of the lead direct to the battery +ve terminal and the bulb should light.
- Start the engine if the bulb goes out you are charging if not then you're not.
If you have a voltmeter connect this across the battery with just your extra lead and ignition off you should have around 12V. Once the engine starts if the bulb goes out you should have around 13.5V to 14.5V (depending on what your alternator throws out).
If you have an LED indicator for the the charging light, it may not provide enough current to kick in the alternator regulator circuit so it may be the LED and its resistor are the problem......
Also simple to replace the diode pack if it has gone...
- With ignition off remove the control lead to the alternator (the thinner lead usually on a 1/4" Lucar connector).
- Connect one end of your made up bulb lead to the now empty alternator terminal. Connect the other end of the lead direct to the battery +ve terminal and the bulb should light.
- Start the engine if the bulb goes out you are charging if not then you're not.
If you have a voltmeter connect this across the battery with just your extra lead and ignition off you should have around 12V. Once the engine starts if the bulb goes out you should have around 13.5V to 14.5V (depending on what your alternator throws out).
If you have an LED indicator for the the charging light, it may not provide enough current to kick in the alternator regulator circuit so it may be the LED and its resistor are the problem......
Also simple to replace the diode pack if it has gone...
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