Truck details:
86 Dodge Ramcharger SE, 360 4x4, auto, tilt, no A/C.
Problem:
Charging system failure.
Symptoms:
Electrical outputs diminished (things light light output, power
windows and wipers are slow, etc). Increasing load on the system makes
lights go dim, stereo to shut off, wipers to slow, and so on.
Increasing engine or idle speed does NOT counter this effect, nor
cause the system to come back up to full power. Vehicle doesn't start
without a jump.
Tests:
Before it died on me I stopped into a Schucks and had them do their
electrical test. The result pointed to the alternator as the failure.
I took the alternator in by itself (the first test was done in the
vehicle). Two bench tests showed the alternator to be fine.
Next I tested the battery voltage with the truck off. Voltage was just
a touch under 12v, yet I had to jump it in order to get it running
again.
With the truck running I checked voltage at the battery again and it
still read 11.4. Revving the engine did not increase voltage.
I then disconnected the voltage regulator and ran a jumper from the
green wire connection to ground to perform a full field test. With the
truck running again, I tested voltage at the battery leads and it read
13. Again, voltage did not increase or drop with engine speed.
My manual indicated the voltage should jump to between 14 and 16
volts, and to only run this test long enough to get a reading. After I
saw the voltage went up 13v but stayed steady, I feel I have ruled out
the regulator as the problem. This is also still under voltage,
correct? Normal voltage should be around 14v. Bypassing the regulator
only bumped it up slightly.
Following the test procedure in my manual, I then disconnected the neg
batt cable and then hooked up a test lamp between the negative cable
and negative post. The light came on. I disconnected the alternator,
and the light stayed on. The manual says this means there is a short.
Next, leaving the test lamp in place and the ignition off I started
pulling fuses to find out what system the short is in. The light goes
off when I pull the fuse at #7 (HORNS) and #9 (DOME STOP LMP). Is it
interesting to note that the test light will come back on if I pull
the headlight switch out?
Now we come to the crux. It would seem I have a short in both of those
circuits. But do I really?
Here's why I ask.
The test lamp is acting in lieu of a direct connection of the cable to
the post. I would expect that the test lamp would of course come on if
I pull the headlight switch out because lights work even when the
ignition is off.
The horn and interior/brake lights are also made to work when the
ignition is off. BUT, I would expect the test lamp to be OFF unless I
was doing something to close those circuits like honking the horn or
actually stepping on the brake or turning on the interior lamps.
I pulled the leads to the horns, brake light switch and interior
lights and still read voltage at those fuse slots AND the test lamp is
on unless I pull those two fuses. I jiggled each of the smaller
harnesses around hoping to see the test lamp blink off but no dice.
My manual does have the wiring diagram, but only shows the circuit for
#9. For #7, 8 and 10 it only shows their presence on the fuse block,
not their wiring.
So what do I do here? Does any of this make sense to anyone? Where
else should I be looking or what else can I test?
Thanks,
R(k)
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