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Message
John Slade
(hit 25 mph last night)
Hi
John,
I would think an LED would
work fine, but unfortunately, the simple schematic doesn't tell us that
much. They're showing a transistor, which should be either on, or off,
like a switch. When no error exists, the transistor (switch) should be
open, and your LED should be off. It's entirely possible that there's more
to the circuit than we
know.
First, are you absolutely
sure you are hooking your wires to the correct terminals? In the
schematic, they show the L terminal above S, but on the picture of the
alt, you'll notice that L is below S. If your LED happens to be in
the S circuit, that would explain why it's on all the
time.
Second, did you deviate from
the wiring diagram in any way other than using an LED in place of a lamp and
diode? Primarily, do the S and L circuits eventually tie to the same point
as shown?
Try putting a normal
diode (just about any diode from Radio Shack) between your LED and the L
terminal. I've always assumed that LED's behave the same as normal diodes,
but I can't say I've ever tested one to see. Nor have I ever used on in
place of a normal diode.
Also, putting a resistor in
series with LED's is a pretty good practice. Finn suggested 470 ohms, and
I imagine that's fine. The resistor limits the current some to protect the
LED, but I doubt it's essential in this circuit for protection. The
circuit itself might expect some resistance, which it was previously getting
from the lamp, so a resistor might do more good than just protection. This
is all speculation since we don't know the rest of the
circuit.
Finally, (as he rambles on) try
temporarily hooking a 12V lamp of some sort with a diode to make it just like
the wiring diagram. You might have an actual problem with your
alternator.
Good
luck,
Rusty
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