Question about 1981 Chevrolet Corvette

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Alternator charge wire getting very hot where it goes into fire wall alternator under load and charging 16 volts but not reaching battery

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Ran bypass wire from alt to starter

Posted on Sep 11, 2009


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Wire diagram for chevy 3500 van

When you say charging,do you mean amp reading or volt reading?Amps should rise when first started then drop.Volts should stay close to constant.The small wire going to the alternator to power the regulator in the alternator is just switched power.If the volts fall under 14 after ten minutes you may need to try a replacement alternator.

Apr 28, 2017 | Chevrolet Express Cars & Trucks

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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:


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


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

How to test a Car Alternator -

Alternator & Charging System Checks -

Dec 26, 2011 | 2002 Lexus RX 300

2 Answers

I think I have an alternator problem? The charge needle on the dash guage is spiking to 16 volts off and on. I put a voltmeter to the battery and it is only charged to about 11 volts. With the engine...

The normal charge of alternator on idling is about 13 to 14 volts. 12 is acceptable but keep in mind it will need attention soon. The needle fluctuates due to the revs of the alternator - there is nothing to worry about. Just look that the charge is always above 12V on idle.

Jul 14, 2011 | 1996 Dodge Intrepid

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Battery is not charging but alternator and battery are testing good

check for bad cell, need a battery tester so it can put load on battery it might read 12 volts till u voltage from alternator batt connection should be more than 12 volts. if its 13 or more be sure wire goes back to battery is charged and connected,

Mar 23, 2011 | 1996 Kia Sephia

1 Answer

I am still fighting an intermittent charging problem on a 1990 GM K1500. It will charge fine then discharge. Doesn't make any difference if in town or on the highway. I've tried three alternators,...

Sounds to me you have high resistance problem , Main power feed to the alternator . Check the power junction block behind the brake booster on the fire wall . There is nothing in the instrument cluster to regulate voltage .B+ voltage to battery symbol when key is on , then when it starts voltage from voltage regulator inside alternator goes back on that circuit shutting off the light . Voltage on both sides of the light cancel's each other out . Yes, i would look for a burnt connector . at the junction block . Do a voltage drop test while the vehicle is running . Voltage Drop Testing the Charging System

Mar 06, 2017 | 1990 GMC Sierra

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Intermittent Charging Problem. I posted a question a couple of days ago about an intermittent charging problem. The volt meter will drop down to 12 volts +- and the battery light will come on and remain...

When you wire it in, run a hot wire directly from the battery to the volt meter (this will give you a more accurate reading) The instructions will come with the volt meter on how to wire it. Just make sure about the hot wire coming directly from the battery.

What I would do first is take off the alternator and go to a parts store and have them test it for free. This will save any additional purchases. Good Luck.

Nov 21, 2010 | 1990 GMC Sierra

2 Answers

I have a 1976 eldorado that when you disconnect the battery when running the car stalls out I replaced the alternator and battery and after a couple of days the battery died the alternator did not keep the...

A 76, huh, let's see, I don't know if that had the regulator in there or not. It sounds like the alt died, but maybe not. It won't run without the alt. And will only last about 20 mins on a full battery. I would take the alt off and get it back to the store to have it checked. That would be the quickest way to tell, just because it is new doesn't mean it is good. Don't keep on killing the battery, it can only handle so many drains. Hope this helps.

Jun 16, 2010 | 1976 Cadillac Deville

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Charging system is not charging. Battery and alternator good. Any ideas?

check the wires for corrotion at the terminals, especcially the ground wire is prone for problems with corrotion, check on both the alternator and the battery and where they connects to the chassis, also check the wires for other defects

Feb 08, 2010 | 1985 Dodge Ramcharger

2 Answers

1994 buick lesabre wont charge

Before, you buy a new Alternator or Battery... Check the Battery with a DC-Volt meter. It should read 12.5 volts or more with the key off. If the Battery reads less then 12.5 volts, have it charged free at Autozone or O'Reiley's auto. If the voltage is 12.5 volts or more, start your engine. With the engine running check the battery voltage again. It should read 13.5 to 15.5 volts. IF YES, Your charging system is work fine.

**IF NOT, and your Battery voltage 12.5 or less, You DO have a charging problem. It must be 13.5 to 15.5 volts!!! 1 - The first thing you want to check is the Battery cables and Battery post contacts. Remove the Negative cables FIRST!!!! Then the Positive, Clean the battery posts and cables with a wire brush!!! There are (3) Large Black cables on the Positive post of the battery, one goes to the starter, one goes to the relays & fues on the fire wall, and one goes to the back of the Alternator Battery output terminal.

Remove and clean the cable, nut & terminal of the Alternator with a wire brush. Then, reconect it tight to the Alternator output terminal. Now, there is (1) Large Black cable & (2) small wires on the Negative post of the Battery. The Large one goes to the Engine Block Ground. The small ones go to the front fender screw on the passenger side car body. Clean them with a wire brush. The most IMPORTANT GROUND is the Large Black cable from the Negative of the Battery going to the ENGINE BLOCK!!! To Remove & wire brush them clean, fallow the Large Black cable going to the Engine Block under the side coil assembly. Remove (3) NUTS & a triangle metal shild. clean all (3) wires & the Bolt & NUTS. Re-assemble very tight!!!

When completed, Reconect the Positive Battery cables firt! Then, the Negative Cables. Make sure they are all making good contact and are nice & tight. Now, check your battery voltage again with the car off! It should be 12.5 volts or more. Re-start the car, Check the battery voltage for 13.5 to 15.5 volts. IF - YES....IT'S FIXED! IF - NOT.... Turn the car OFF & look for a small black conector that plugs into the side or under the Alternator. It will have only (1) small RED wire going to it.
Very carefully, stick a straight-pin in the red wire & let the pin come out the other side. Don't let it touch any metal !

Start the car & let it run. Now put the (black) lead of your DC-Volt-Meter on the Negative of the Battery. Then, put the ((red) lead of your meter on the straight pin. It MUST have 8.0 to 12.0 DC-volts there !
IF - YES... The regulator inside the Alternator in BAD. (REPLACE) the Alternator. IF - THERE IS NO VOLTAGE there... Then, the red wire is bad... or the (P C M section) inside the ENGINE CONTROL MODULE is BAD!

The Alternator is about $100.00, The red wire is about $2.00, But the ENGINE CONTROL MODULE is about $400.00 plus from a dealer. Only, about $170.00 from autozone and about $125.00 from a wrecking yard.

**** NOTE **** If your Engine Control Module is bad, Look for my INFORMATION on FIX-YA, "HOW TO REPLACE THE ECM on a 94 BUICK" Thanks and GOOD LUCK !!!

Nov 09, 2008 | 1994 Buick LeSabre

1 Answer

2003uburban not charging

make sure you have power to the back of the alternator and make sure you have power from the plug

Oct 22, 2008 | 2003 Chevrolet Suburban

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