Actually, no. You can still get correct voltage readings, but that does
not mean enough current will flow through that weak point to supply
the proper amount of "current" that item requires. He may indeed find
a bad connection which may be "open" hence the improper or no reading.
I speak from experience in voltage through a device/wire/cable will
not always supply the appropriate current to operate a device. For
example, connect a small gauge wire (not cable) to your starter in place
of the standard gauge. You will find voltage when checking for voltage
only. But as soon as the demand for current is needed, that wire can't
supply the needed capacity. Fire hose vs. garden hose. I'd suspect
"bad" connections rather than "open" connections.

Signature
_________________________
Laszlo Almasi
Carolina Watercraft Works, Inc.
"In the battle between money and love, money will always triumph"
I may have to change my signature......on second thought, I was right the
first time.
> Actually, you are the one who is incorrect. If you read what he wrote,
> you
[quoted text clipped - 17 lines]
>> > Bad connection will be between the point where voltage was high and
>> > where it was low.
> Actually, no.
Once again, if you read it you will see that you are incorrect. In order to
perform the checks required, the lights have to be operating and if the
lights are operating, any voltage drops (the only thing that can limit the
current) can be discovered by his method.
> You can still get correct voltage readings, but that does
> not mean enough current will flow through that weak point to supply
> the proper amount of "current" that item requires.
You cannot get correct voltage readings if the required current is being
restricted. This is made obvious by Ohms Law. The only way the "weak" spot
can reduce the current would be by dropping voltage due to resistance and
that would be detected by the suggested method.
> He may indeed find
> a bad connection which may be "open" hence the improper or no reading.
If the connection were open, the light would not light at all.
> I speak from experience in voltage through a device/wire/cable will
> not always supply the appropriate current to operate a device.
While this is true, a voltage drop would be seen on the undersized wire and
I have been doing this for over 30 years.
> For example, connect a small gauge wire (not cable) to your starter in
place
> of the standard gauge. You will find voltage when checking for voltage
> only.
But this does not duplicate the method suggested as the starter is not
operating as the headlights would need to be to perform this test.
> But as soon as the demand for current is needed, that wire can't
> supply the needed capacity.
And if you were to then measure the voltage at the starter, you would see a
massive voltage drop due to the higher internal resistance of that thin wire
which is exactly what the suggested method is looking for. Not so much a
massive drop as in your example, but a significant drop due to a bad
connection somewhere.
> Fire hose vs. garden hose. I'd suspect
> "bad" connections rather than "open" connections.
Of course it is a bad connection since the light does work, it is just dim.

Signature
If at first you don't succeed, you're not cut out for skydiving
>Actually, no. You can still get correct voltage readings, but that does
>not mean enough current will flow through that weak point to supply
[quoted text clipped - 7 lines]
>supply the needed capacity. Fire hose vs. garden hose. I'd suspect
>"bad" connections rather than "open" connections.
No, Laslo - you are WRONG. If you know anything about DC electricity
you would understand.
And we were looking for bad connections, not opens. We are testing
UNDER LOAD - so we WILL find that piece of garden hose spliced into
the fire hose.
As far as your starter example, check the voltage at the starter with
it cranking. You WILL see a reduced voltage.
Your big problem appears to be you cannot read.