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do you have an old alternator that you
like to test just kick around the shop
here I'll show you how to do it okay so
what we got here is an 82 for for
alternator came on 99 to 2006 GMC trucks
this great alternator rated 140 amps the
key thing about this alternator is that
it gives you most of all your current at
idle speed so you don't have to rev the
alternator or your engine up to 3000 to
make a lot of current so all you need to
test the alternator so I got a plug here
factory plug it's a four pin plug only
three of them are used the only one you
need to worry about is the brown wire so
this plug essentially there's letters
associated to the plugs plug ports so
you got PL is so pob for it's mostly
used on diesels
it'll be essentially a rev counter so
this is how your diesel vehicle that
tachometers hooked up it's hooked up
through this wire this came off a gas a
gas motor so this wire wasn't used this
here's the L it's for the lamp so your
charging indicator dummy lamp this was
this wires for PL I this is this will be
usually an ignition wire so hooked up to
12 volts mostly in the pulse-width
modulation newer trucks where the ECU
controls the field of current this wire
will be used this wire here actually GM
that didn't use it that CS wire sensing
wire so if you want to account for a
voltage drop you would run a wire here
to wherever your voltage really matters
and then that'll count for the voltage
drop
so the only wire you're concerned about
is the brown wire here that'll be the
lamp wire this is the only hookup you
need to test the alternator so I got my
voltage meter here hooked up to the
battery we'll turn it on okay so we're
at twelve point five three volts just
push it to tears you guys could see okay
twelve point five three volts now I've
got a light bulb here so get yourself a
low five watt light bulb run a jumper
wire from the brown wire to one side of
the light bulb the other jumper wire I
got going to the switch this is just for
so that I could control when it's going
to charge not but you don't need to hook
it up to this switch and then go to the
positive post on the alternator do not
hook this wire up to the positive post
directly without a load because you will
fry the voltage regulator it needs to
have a load on it or in series with it
okay so give yourself a drill with a I
got a thirty one thirty seconds socket
on here so right now I got my switch off
so nothing oh it's not going to charge
when I spin the pulley here so we're at
twelve point five three volts so I'm
gonna start spinning the pulley
[Music]
nothing's changing okay so now I'm gonna
flick my switch okay so this is your
dummy light so this is telling you the
alternators not charging now you'll
notice as they start turning this pulley
that light will go dim until it's all
the way out and that's when it'll start
charging so let's try it here
[Music]
okay I'm not spinning it fast enough let
me kick it in the second gear here
okay I'm not able to spin it fast enough
let me get another battery you need to
be spinning us pulley at at least 1500
rpm so we may have a hard time but we're
at twelve point three volts I'm turning
a switch on go little batteries at
twelve point one zero or two so we'll
start spinning it not charging not
charging
you'll notice if I release the trigger
the light will come back on saying it's
not charging
[Music]
now if I turn that switch off listen for
the the speed of the motor on the drill
here it'll really slow down once I
flicked a switch at high speed showing
that the alternator is putting a load on
the drill because it's actually creating
current generating current thoughts full
power on the drill I'll flick the switch
it's really giving her no click the
switch no longer charging drills going
at full speed
[Music]
okay so that's essentially how you test
the alternator like I say all you need
is one wire the brown wire while GM uses
Brown but it's essentially the El wire
which is light indicator light so take a
jumper from that wire go to your bulb
again make sure you got if you don't
have a bulb get at least a 50 ohm
resistor put it in series with these two
jumpers otherwise like I say you'll fry
the voltage regulator so the other end
of the bulb when my case goes to switch
but that's not necessary the other end
of the bulb will go to your positive
ignition source
now these newer GM's they don't have a
incandescent bulb they actually have
this goes to your computer so the
computer will ground this bulb on your
dash telling you that you're not
charging but they use pulse width
modulation modulation through this wire
here so that's essentially sine waves
and that will regulate the field of
current that this alternator will output
but on an older truck like say a 98 or
whatever then all you need to run this
alternator again is this one brown wire
one more thing I wanted to touch on that
I forgot to mention is these newer
trucks like the GMT 900 platform 2011
and up and stuff they they really use a
pulse width modulation to actually vary
the voltage output of the alternator so
at idle they'll develop put maybe
thirteen point two volts just so they
don't put a huge load on the motor and
on highway or it ever though output I
think it's even twelve point eight volts
or something it's very low now this this
is okay for the average user but if
you're running car II all car audio and
stuff you're not gonna like this so what
I've heard is this pulse which pulse
width modulation wire if it's senses and
open so if you cut this wire the
alternator will run full field so it'll
default
- its 14 and a half volts so that's very
common in the car audio department if
you're like I say if you're running subs
and stuff you don't want that twelve
point eight volts going to your subs cut
this wire
you should have 14.5 volts all the time
so I got a different battery hooked up
now
the other one was dead which is probably
why it didn't want charged all that good
so let's just do a quick we'll turn it
again and see how many volts we could
get bulb on okay 12 point 7 volts
and see your belt started slipping then
your lights would come on there she goes
yeah so that other battery was just
straight dead so that's why it was
taking up so much current that the I
couldn't spin the alternator fast enough
to get some current flowing there Makua
maintaining the voltage so there you go
we got 14 volts out of her again I'm
probably not spinning it quite fast
enough but if I had it on the car it
would spin much faster again hope you
guys enjoy this video and
