Paul.Kort@marconimed.com wrote:
>
> I'm not an electrical engineer but my guess is amps! I had a headlight that
> refused to do more than glow. I switched bulbs, still just a glow. Meter
> showed 12 volts but on closer inspection I found that the PO had spliced the
> wires under the fender and one of the wires was down to one or two starnds.
> Enough I guess to show 12 volts on a meter but not enough to light a
>headlight!
> New connector and wiring did the trick. And now I have great lights and can
> actually see where I'm driving at night. Maybe the 45 amp GM alternator
>helped
> with that too!
>
Yes, that's exactly right. It's about amps. And volts. And resistance. And
power. (Scotty! Give me more POWER!) THese are interrelated so that you can't
really talk about one without involving the others. Think of your car's wiring
as a plumbing circuit. The pressure of the water is analogous
to voltage - electrical pressure. The amount of water flowing is the amperage.
Any restriction in the water flow is resistance. Obviously, if your
resistance is constant and the voltage is higher, you'll push more water past
that resistance, giving a higher flow rate - more amps. Similarly, if
your voltage is constant and the resistance is lower, you'll have more amps -
more flow. It's not a perfect analogy, of course, because current flow in an
electrical circuit happens at something reasonably close to light speed.
(Sorry - no warp drive.)
If you have a restriction in the line such as a wire frayed down to a few
strands, corrosion or just plain grunge on connections, then you will reduce
the flow of electricity. (True whether the restriction is on the hot side or
the ground side of the circuit.) Fewer amps means less power (power
is voltage times amperage) which means dim headlights. But your alternator is
putting out the same amount of power! Where did that power go? It didn't get
to the headlights. We know from the first law of thermodynamics that power can
never be created or destroyed - it can only change form. So
where is it? It turned into heat at the point of resistance. Hence Tom's
warnings about wiring harness meltdown and fires! That's why it's a bad idea
to run high power add ons to your old roadster wiring.
So why did the voltage meter measure a full 12 volts at the headlight
connection? Well, if you put a pressure gauge on a faucet in your garden, and
just barley crack open the valve (allowing some contact with the water, but
very restricted) it will take the pressure gauge a few seconds to register
the full pressure, but register it will. Now take off the pressure gauge and
try to hose down your patio. It ain't gonna work, is it? You don't have
enough pressure! Now you've got a loaded circuit. That's why a test light
needs to be in your tool kit along with that voltmeter.
--
Mark van der Hoek
Houston, for now
"They that can give up essential
liberty to obtain a little temporary
safety deserve neither liberty nor
safety."
-- Benjamin Franklin
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