Alternator warning light--no glow

[Jameel]

'79 SC Coupe.

Just got this oil gauge back from the repair shop and hooked it up. The alternator warning light is not coming on. Here's what we know and what we've tested. (it's my brother's car.)

-running LED's from Car Magic. Bulb works fine--tested aok.
-tested the housing by pulling it from the gauge and testing with the LED bulb directly to a 12V batt. Bulb glows.
-tested the terminal on the bulb housing coming from ignition switch #15--it's getting 12V with the switch on
- tested battery. 12V engine off
- tested battery. 13.6 volt at 1500 rpm, drops back .1-.2 volts at idle.
- pulled the plug from the wiring harness going to the voltage regulator and put a meter on the blue wire with ignition switch on (engine not running.) Got .5V Not sure what this is supposed to be...

It seems like the alternator is making energy and charging the battery. Only thing I can think of is the blue wire from the alternator to the gauge has lots continuity. All the wires in this car are in really nice shape. But anything's possible I guess.

[oilman]

I just installed the car magic LED kit.... love the brighter dash! I don't think the kit includes the alternator warning or low oil pressure lights .. there should be separate (smaller) bulbs in black plastic housing for these lights.

Dave,

[Lyle O]

If you're not getting the alternator light when you turn the key to the on position, before the starter is triggered, it is either the bulb itself (which you have verified functions when you apply 12 volts to it), the wire to the bulb, the voltage regulator and its wiring/connections, or the alternator and its wiring/connections. Drive to a Auto Zone or Advance Autoparts, and they can do a quick, free, alternator/charging system check for you to see if the alternator is putting out enough juice. If it isn't, the light won't light. If the system checks OK, it is the wire to the bulb. I just went through this on my '87 (shouldn't be different from the SC) and it was the alternator...

[Jameel]

Problem solved! Grabbed a fresh incandescent bulb from the glove box of my '69 beetle and swapped it with the LED. Lights up and goes out when it should now.

Since found a few threads describing this exact situation.

[porschenut]

Remember that an LED is a diode, which is polarity sensitive. Hook it up with the wrong polarity and no current will flow through it. Perhaps this was the problem. Incandescent bulbs don't care about polarity.

[grizzfan]

Man you are lucky with no alternator light. Mine glows all the time!!

Tom