In a message dated 97-10-27 09:28:11 EST, flake@a3115jmf.atl.hp.com writes:
> One trick when debugging a fuse blowing situation is to
> connect a test lamp across the blown/missing fuse. If
> there's a connection to ground (either a short or a
> normal load such as a light) the test lamp will be on.
> Your process in chasing the short is to find the wire
> or whatever which when moved will make the test light
> go out. Easier to see than a meter, and beats the
> heck out of feeding it good fuses!
Joe:
This is an excellent suggestion! However, there is one caveat which needs to
be expanded upon. As you pointed out, to a test lamp, almost every device in
a car looks like a short to ground. If you hook up a test lamp in series with
a turn signal bulb, for example, the test light will quite happily light up
as if it were connected directly to ground, yet the turn signal bulb will
light very dimly, if at all. If you are looking for a ground, it will be
necessary to remove ALL the bulbs from their sockets first.
As another example of this, does anyone care to guess what would happen if
you placed one of the small lamps from a dashboard gauge in series with the
battery cable feeding the starter, and then turning the key switch to the
start position? The intuitive answer is that the bulb would pop instantly,
but the correct answer is that the bulb will light up perfectly well, with no
damage at all, and the starter will not know anything happened. The internal
resistance of the starter windings is extremely low compared to the bulb.
With 12 volts applied, 11.9999 volts (approximate!) will be dropped across
the bulb, and the remaining 0.0001 volt will be across the starter.
If you are working by yourself, you can replace the lamp with a buzzer, so
you can work at the back or under the car, where you couldn't see the lamp (
the constant sound of the buzzer can be an irritant, so get one with a
pleasing sound!).
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition
'68 MGBGT---organ donor for the '74
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