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Mopar
Headlight Dimming |
Mopar Headlight Dimming |
Dim Headlight Syndrome
Since we have had so many questions
about dimming headlights when the engine is at idle, I have decided to
explain the problem here and hope it will help allot of you out.
The headlights (and all of the other lights on the car) go dim for
only one reason, that's because the system voltage drops below the
normal voltage of 14 volts. Voltage is electrical pressure just as water
pressure makes the water come out of a faucet. The greater the pressure
(voltage), the faster the water comes out. Loose the pressure (voltage)
and the water come out slower. Loose electrical pressure and the lights
get dimmer. Amperage is electrical volume and since your headlights and
standard electrical options are less than the amperage (volume)
capabilities of the alternator, voltage should remain in the normal
range (14 to 14.4 volts). So, why does the voltage go below normal? First thing to be sure of is that the wiring is not restricting the flow
of current to the system. This can be done using a digital voltmeter. Connect the positive(+) of the meter to the battery stud of the
alternator and the negative (-) of the meter to the POSITIVE of the
battery. Run the car with the lights on (to create a load) and read the
meter. You should not read more than .3 to .7 (that is tenths) of a
volt. Do the same with the negative side of the charging system. Connect
the negative (-) of the meter to the alternator case and the positive
(+) of the meter to the NEGATIVE battery terminal. More than that and
you have wiring that is not allowing normal flow of electricity. (Hint,
did you check the bulkhead connector for a hot or burned connection?)
Now for the more probable cause of your problem. The same type of
Chrysler alternator was used for many years and all had the same
physical shapes. However, the electrical characteristics changed over
the years. Before 1969 the alternator was a rather low output (37-42
amps) and was used with a mechanical regulator. The rotor installed in
these alternators had a field current of 2.3 to 2.7 amps. In the later
70's the windings in the rotor was changed and had a much higher
resistance. Over the years the alternators have been rebuilt so many
times that the rotors generally don't get tested for the correct
application and a higher amp rotor could be installed in an alternator
that it was not designed to be in. A higher output alternator will give
you more amperage capacity, but only at higher engine RPM's and will
usually not do as good as a lower amp alternator at low engine RPM's. Later model high output alternators are designed to give good output at
low & high RPM's and the engine idle is usually 200 -300 rpm's
higher than your classic car. So the moral of the story is that there
is a good possibility that the alternator on your car was not rebuilt
with the correct parts to operate as it should on older cars. If the
same alternator was installed on a 70's car with an electronic regulator
and a few hundred higher engine RPM's, you would never have a problem.
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