In a message dated 7/5/99 11:25:38 PM Eastern Daylight Time,
Webmaster@infinitefx.com writes:
> I got some responses on my ignition light problem but I will refresh for
> you.
>
> Hook battery up. Ignition light comes on with the key turned OFF. Turn
> the key ON and the light goes out. None of the wiring leading to the
> alternator has ever been changed. I did as Randall suggested and unhook
> the wires and try again. The light went out. Plugged the big plug (3
> wires) back in and the light was back on again. I have 4 wires total.
> 3 in the harness and a single that goes on by itself. If I leave the
> battery connected I get a terrible discharge that kills the battery in
> about 2 days. I need more ideas.
Don,
It's almost certain that your alternator/regulator is bad. I'll explain. In
order for the warning light to come on, there must be about 12 volts
difference on one side of the buld to the other. Normally, when the key is
off and the alternator is not turning, you have zero volts on bith sides of
the bulb. When you turn the key on, but before the alternator is up to speed,
you have 12 volts on the ignition key side of the bulb, but zero on the
alternator side, and the bulb lights. When the alternator is up to speed,
there is 12 volts on both side of the bulb, for a difference of zero, so the
bulb is out.
If the alternator should die, you will have 12 volts on the ignition side and
zero on the alternator side, and the bulb will light to warn you.
Why is your bulb lighting up with the key off, and not on? You have a short
in the alternator which is placing 12 volts on the bulb at the alternator
side. With the key off, you have zero volts on the key side and 12 volts on
the alternator side - the condition for the bulb to light. However, in order
to have the bulb light, you have to have a current path as well. In your
case, the current path is what is causing yur battery to die. The key side of
the bulb is also connected to your key-switched electrical loads - gauges,
turn signals, etc, and the ignition coil. The resistance of the alternator
warning light is high enough that the gauges won't register, evern though
current is flowing through them.
Try this to prove (or disprove) my theory -- remove the fuse between the
white and the green wires in the fuse box, pull the lead from the oil
pressure switch, and disconnect the ignition coil. If you haven't added
wiring to the car, I bet your alternator light will be out with the key off.
Another way to do this would be to disconnect the brown/yellow wire from the
back of the warning light and measure the voltage on this wire. It should be
zero, but in your case, it will be battery voltage.
Check out: http://www.vtr.org/maintain/alternator-overview.html
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://members.aol.com/danmas/
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74
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