Alternator out put and out put on automotive battery terminals ,what is the permissible difference in volts? What are the possible reasons for a reduced output on battery terminals (eventhough alternator is ok)such that battery does not get charged?

BATTERY LIGHT!: Hello All! Today I Was Driving in a Rainstorm, and... (2carpros.com)

Compass alternator won't charge... bad PCM? ' My Jeep Compass Forum

Compass: I replaced the alternator in my 2007 Jeep Compass (justanswer.com)

These link talk about Issue with fusible link and wire to pcm or pcm.
Just a thought check for good clean grounds, tight clean connection and battery fully charged.
Not sure but hope this may help in some way. Good luck

Its a diesel and didnt know the alternator controlled the RPM ,i thought it was controlled by the wire going to no3 injector on older models

Vehicles: any failing to keep its battery charged.

A vehicle unable to charge its own battery has one of 4 problems:
(a) alternator failure
(b) voltage regulator failure
(c) battery failure
(d) wiring problem between battery and alternator/voltage regulator.

One most modern vehicles (including 2002 Lexus RX300 - 2WD and AWD), the voltage regulator is an integral component of the alternator and is not separately serviceable.

In the US, one can get a free "charging system diagnosis" from the popular auto parts chains: AutoZone, Advance Auto Parts & Pep Boys. You needn't remove any parts from the car to get this diagnostic, since they can attach a diagnostic meter to the charging system in the parking lot. This diagnostic aid will tell you exactly which component has failed - battery, alternator or voltage regulator.

In case the vehicle is immobile, one can DIY (do it yourself) the diagnosis.
(a) inspect the wiring for corrosion/loose connections/loose connectors/etc.
(b) check alternator belt/pulley - if drive belt is properly turning the alternator pulley (no slippage/misrouting/etc.), then the mechanical tests are complete, and you'll need to continue testing the electrical performance of the charging system components.
(c) first component to test: battery
DIY test 1: remove battery from car and put battery on a 120VAC automotive battery charger and charge it fully (or just check it in the car with motor off, since the car's charging system is a type of automotive battery charger).
test parameter: a fully charged lead-acid automotive battery should read 12.45 volts on a VOM/DMM
DIY test 2: disassemble battery out of car after driving it to one of the auto parts chain stores (Advance/AutoZone/Pep Boys) for a free battery test. These testers will test the battery under load, which is not possible with just a DMM.
(d) if wiring is good, and battery tests good under load, then
the failed component is the alternator/voltage regulator - by process of elimination.
(e) DIY test 3: direct alternator/voltage regulator test (car must start and idle successfully to perform this test)
Start the car, and put a VOM/DMM across the terminals of the battery. Since the car is running, you'll be reading the output voltage of the alternator and not the output voltage of the battery. The acceptable ranges for alternator/voltage regulator output are:

ALTERNATOR CHARGING VOLTAGE

Most alternators that are charging properly should produce a voltage of about 13.8 to 14.2 volts at idle with the lights and accessories off. Always refer to the vehicle manufacturer's specifications. Many Asian vehicles, for example, have higher charging voltages of around 15 volts.

When the engine is first started, the charging voltage should rise quickly to about two volts above base battery voltage, then taper off, leveling out at the specified voltage.

The exact charging voltage will vary according to the battery's state of charge, the load on the vehicle's electrical system, and temperature. The lower the temperature the higher the charging voltage, and the higher the temperature the lower the charging voltage. The "normal" charging voltage on a typical application might be 13.9 to 15.1 volts at 77 degrees F. But at 20 degrees F. below zero, the charging voltage might be 14.9 to 15.8 volts. On a hot engine on a hot day, the normal charging voltage might drop to 13.5 to 14.3 volts.

Here are the full specs for installation of the 2002 Lexus RX300 alternator - you may be able to check these specs yourself (with a torque wrench), or pass them along to your mechanic.

Note: the VIN 8th digit should be "F" for the 2002 Lexus RX300 (2WD & AWD)

2002 Lexus RX300 (2WD and AWD) - 3.0L Engine, VIN "F" SFI DOHC

Alternator

Drive belt. Tension the belt to 170-180 lbs. for a new belt or 95-135 lbs. for a used belt.
Adjusting alternator lockbolt. Tighten the bolt to 13 ft.-lbs. (18 Nm).
Alternator pivot bolt. Tighten the bolt to 41 ft.-lbs. (56 Nm).

Glossary of acronyms
--------------------------------
DIY = do it yourself
DMM = Digital Multimeter
DOHC = Dual Overhead Cam
SFI = Sequential Fuel Injection
VOM = Volt Ohmmeter

References
----------------
How to test a Car Alternator - todayifoundout.com

Alternator & Charging System Checks - aa1car.com

Charging is sufficient you want 2 volts above battery, for that dash to be on there will be a terminal on the alternator that is not connected it is a single wire you will need to make sure that it is connected,the terminal have tendency to break off and sometimes people who put the alternator on forget to put that terminal on they just dont see it it a wire by itself

From what you have described either the replacement alternator or regulator are faulty.all 1985 model here have the reg built into the alternator.Put a voltmeter across the battery terminals while running.volts should be 14 to 14.8 if it is being charged correctly,12.8-13.9 if it is poorly charging and less if it is only running on the battery.I assume that the fanbelt is tight and not slipping.There are several other reasons that can cause this fault but establish the basics first.Make sure that the main feed wire from the alternator to the battery is fitted onto clean terminal and isnt broken internally.To test this you can carefully check volts at the alternator terminal end,be careful not to arc out on anything metal while doing this.you may blow the charging fuse(check this anyway as part of test).the volts should be the same as reading from the battery.If it is lower,twist the wire about while reading and see if it changes.It will either need replacing if faulty or try new terminal ends first.Make sure that the replacement alt has the same plug configuration as the one you removed.Honda have a few different plugs that switch the trigger wire around(whether round or rectangular)Hope this helps you.if not get back with your test results and we can work together on this

Here is a easy way to do it have a voltage tester on hand///multi meter put the positive to positive and negative to negative you should have engine running your voltage reading should be 12.79 up to 14.29 anything under bad alternator anything over 14.29 is bad that's over charge that usually cooks the battery.And truck not runnig test the battery same fashion your reading should be 12.79 up to 13.29 is good under battery no good.Good luck to you

take it off and then go to bosch agent and hand this junk in and get a genuine bosch exchange unit ,then when fitted start car and disconnect neg terminal and the engine will keep running ,job done

I don't know where you checked alternator out-put? I'd check at the alternator bat terminal and across battery posts, both, the reading should be close to the same.
It's possible when you took battery cable loose to install ammeter in series, a module may have shut off? Use a jumper wire to keep connection till you get the ammeter hooked up. Just my opinion.

It may not be the starter. The battery could have a weak or dead cell in it and not holding a charge.
The alternator could be bad and charging the battery.
If you have a volt meter, or can get one, with the car running, put the leads from the meter to the battery terminals, red positive, black ground.
Put the meter switch to 12 volts. If the meter reads 14 to 15 volts, the alternator is ok, below that it isn't charging. If it does read 14 to 15 volts, replace the battery.
By the way, the starter is ok, or it wouldn't have started with a jump.
It's more a battery/alternator issue. Clean the battery terminals first and see if that makes a difference.

On some of the older style GM's you can take that brown wire and cut it and take the end leading from the alternator and hook it directly to the hot terminal on the alternator and just leave it hooked up and it will work. But I have ran into the occasional problem where leaving it hooked up will drain the battery when the vehicle isn't running. Hope this helps..