Battery Discharge Battery, Alternator, and starter are all good. My battery discharge light shows when I hit 3000rpm. I assume it's a short somewhere. Any suggestions on where to start looking?

check body ground straps

Have the battery,alternator checked & & have it checked for electrical shorts.

Check the alternator output with a multimeter. You should get14volts out of the alternator (I purchase brand new alternator and sometimes there no good), it happens, check the big wire coming out of the alternator, if you dont get at lease 14volts it's no good (it's got to generate more than 12volts).good luck.

taking a cable off the battery while the engine is running is a guaranteed way of killing the alternator . The alternator has not been checked properly as it has to be on the vehicle to test all the cables and regulator. If the battery was tested with a multimeter then it has not been tested correctly as it is done with a load tester to determine if the battery is capable of holding a charge under a discharge load.. Batteries can discharge internally as well as from a current flow though a completed circuit Ie-glove box light on --boot light on -- door light on relay coil shorting out . Take it to an accredited auto electrician and have the work done properly as it saves a lot of heart ache.

1. Is the lights glowing correctly?
2. check the battery contacts once again re fix them.
3. check the polarity of control unit (Rectifier circuit).
4. check the charging current without load. if it is good it is to be expected. when there is 20 amp load.

did you try to jumper cable start car?
that is a NO CRANK issue, no car starts (cept mine, its an M.T) with out the starter motor working, (mine can be push started or hill started)
Jumpers fix issue?, so bad/dead /discharged battery.
so????
so is the IMMO light showing IMMO blocking, , you ever read the operators guide and see IMMO rules>
lamp on, lamp off, lamp flashing... all have meanings.
the IMMO cuts fuel, not the starter,
so its not IMMO. Its a bad starter system. (it is a system of parts)

no crank has many causes. the tests are easy with a voltmeter.
a $20 volt meter can save you the cost of a $140 battery.

It can be a free fix. (clean the battery lugs yet>?) ask how.
to start the engines (assume engine is ok and EFI ok, and spark ok)
the start system can fail like this.

1: A dead battery ,bad bat., or only discharged, a voltmeter solves this riddle. (ask how)
if only discharged, then charge it. and find cause of discharge ,1st or it will repeat.
the order here, counts.
2: bad battery to starter cables.
3: bad starter solenoid, or starter. we hot wire IT.(ask)

(fails? , bad starter,assumes battery side is good,first)
hot wire fails.
I hit the starter casing with a hammer bam, it now works.

4: starter cranks hot wired. it's good. (test passes so i then find the bad KEY line. cause,,, we now have problem cut in half.

5: the KEY line is that wire that runs from KEY (ST) to the starter , small wire.
on an A/.T car, (auto/trans) car, the key line passes thru the
PRNDL switch on tranny. so wiggle the gear shift. cranks now>?
try cranking in Neutral. some cars allow this, and
the Neutral side of the switch will like new, and car cranks.

that was the long answer.
here is the short.
Take it in. call the auto club.
guess, i guess,?
1: left head lights on.
2: battery lugs never cleaned.
3: battery died.

dear you should test , the charging while light On, its must be 13to 14 volt ,alternator will be noisy when more charging , if there any short circuit when use head light ,

your battery isnt what was bad to begin with, if it is discharging either change, or have your alternator rebuilt.. thats your problem 100% sure

The most likely cause if you have changed batteries and replaced the alternator is that you have something that is an electrical drw when the car is shut off.

I assume the battery goes down while the car is sitting?

If it goes down when you are driving, it is likely a different problem.

If you don't have a multimeter to check for current draw when everything is shut off, an easy test to remove the negative battery cable and let it set the time it takes to discharge.

Then hook it back up and see if you have a full battery. If it doesn't go down with the batteryt cable disconnected, you either have a short somewhere or there is something left on (like a glove compartment or trunk light) that is draining the battery.

I assume you checked for the obvious things like brake lights staying on when the car is shut off (brake light switch problem).

Check alternator for charge,somebody was boost and fray diode inside alternator,start car when car is runing remove positive cable if car stop you need new alternator