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ignition light

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flynns tr 7
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Postby flynns tr 7 » 13 May 2009 21:56

A few tips on charging lights .Even if you connect a mulimeter across the battery and it reads 14 volts this does not mean your alternator is charging the battery.What you normaly see is a voltage between 13.5 to 14.5 this is to give a potential difference between the battery and the alternator to ensure the battery will charge eg the one bieng greater than the other.it also gives ann indication that the voltage regulator is also working.However what also should be checked is the amount of current also being generated this cannot be done with a conventioal multimeter becuase they only go up to 10 amps most alternators can generate upto 80 ampsand you have to connect the meter in series (brake into the circuit).to check the current amps what you need is a clammeter that fits around the cable and measures the current generaly about 10 amps with no load and with a load cshould increasee.So in some cases yes the voltage is correct but in my experience you tend to find thier is insufficent or no current being produced.Connecting an oscilloscope can also identify alternator faults by interpreting the pattern produced and referencing to the voltage and current produced.

bmcecosse
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Postby bmcecosse » 14 May 2009 22:12

If the battery shows 14 volts with engine running it IS being charged !! Simple further check - switch on heater fan and headlights - should still show 14 volts provided the revs have been lifted slightly. If alternator not charging, the volts will be ~ 12 volts - 12.5 at best!

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MillerScottLite
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Postby MillerScottLite » 28 Jun 2009 14:51

I took my battery back and they did a test to it and it was still good according to their machine. My ignition light is still on and when driving the other day the light started to blink on and off. I am able to drive with the lights radio all on and have not had any problems starting. It was showing 14.2 V when running as I posted in my earlier post.

Any thoughts?

Thanks

Scott

jclay (RIP 2018)
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Postby jclay (RIP 2018) » 28 Jun 2009 15:24

OK, there should be a small Brown/Yellow wire on the back of the alternator. Disconnect that and see if the light goes out.

Now, power goes from the printed circuit film to the bulb, then through the Brown/Yellow wire straight to the alternator where it is grounded when charging.

If the light is still on with the Brown/Yellow wire disconnected at the alternator, THEN the Brown/Yellow has rubbed against something and worn away the insulation. It is making light (dim light) and/or intermittent contact (flashing light) with a piece of metal on the car.

Finding it could take a while, but I would start in the engine bay and work back to the dash. I had a wire on my old suburban that did this. Every time I would turn on the left blinker, the back window would roll down. Try finding that on a dark winter road!



jclay

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MillerScottLite
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Postby MillerScottLite » 28 Jun 2009 16:11

Jclay. When my light was blinking it was a very deliberate fast off and on, not intermittent. My alternator has a modular plug with 3 wires coming out of it, a big brown wire a small brown wire and a small brown/yellow wire. It is a 1980 AC 5 speed convertible.

The light also shows signs of draw like if I put the blinker on, turn up the radio, or turn the lights on. It gets brighter with each.

Scott

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