>
> Hey fellow SOL,
>
> The ignition lamp on my '75 MG Midget comes on when I touch the brakes, and
> blinks when I use the direction signals. It usually has a dim glow on a
> constant basis and sometimes it goes out completely (but not often). Do I
>have
> a short in my electrics? If so, where is the best place to start looking?
>
Not a short, but rather high resistance somewhere.
The ignition light is wired between the switched side of the ignition switch,
and the output of the alternator. When there is a voltage differential between
these to points, the light glows. The bigger the difference, the brighter the
light.
Normally, this differential is caused by the ignition being on, and the
alternator not charging. This is the intended purpose. However, the reverse
also happens. If the alternator is charging, and it's internal voltage is
higher than that available at the ign switch, then the light will glow. This
is why the light comes on and flickers down when you shut the key off.
First check that the body and the engine both have a good ground. Then, using
a volt meter, check voltages at various points in the system. Do this with
the engine running, and a load on the ign circuit (turn, brake, possibly
heater and wipers). Check (in order):
alternator output (big brown wire on alt)
battery side of the starter solenoid
brown wire in ign switch plug
white and white/green wires in ign switch plug
white wire bundle on fuse block.
This is the general path the current takes. If I had to pick something
blindly, I would say you have an ign switch problem. If so, the voltage
at the white or white/green wire will be lower than the brown by a few
volts.
BTW, other cars do this a lot more than Brit cars. Volvos are notorious
for this. My Lancia has such a hodge-podge assortment of poorly designed
harness connectors that I finally punted and put a diode in the light
wiring to prevent this backfeed. :>
Randy
randy@taylor.wyvern.com
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