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Hi, I posted on here a couple months ago with a similar question. Basically my battery is draining while the engine is on and I would really appreciate any advice on how to diagnose it. I realized this the hard way when the car died in the middle of an intersection and I had to push it through.

In the last month I've replaced the alternator and the battery (both of which which needed to be done) and in the last year replaced the starter motor and O2 sensor as well as had some work done on the exhaust system and carburetor.

So even with a virtually brand new alternator and battery, the voltmeter will drain until the engine dies. I've noticed this is especially true when the headlights are on. Also, the battery doesn't die when the engine is turned off so I know its not the battery.

Thanks for any help!
 

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Hi
put an ammeter inline with your positive battery terminal. you should see some draw if you have a clock or radio with memories.
Next, go to your fuseblock and pull the radio/clock fuse.. check the meter.. still have a draw??

Proceed to the next fuse.. pulling them one at a time until you have no more draw on the meter.
When you pull a fuse and the indication on the meter goes away, it is that circuit that is the problem
This will narrow down to at least what circuit is causing the drain..

Ed
 

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Ed, Read it again, His issue is with the car running, not a drain with it parked and sitting.

alampshadedream, I'm with Leo on this one. Your system NEEDS to be tested. With the Items being replaced with new, you have an issue that will require a little more than a question and answer on a forum. You may have wires hooked up wrong or something along those lines.
If the system IS CHARGING with the Motor running, yet it still drains, that's one HE** of a DRAW. Could be the NEW ALT. is Bad. NOT UNHEARD OF WITH NEW OUT OF THE BOX.
Have the system checked. We could guess on this for weeks. At least get a direction to go with.
THINK about it ~ Alt. charging at 55 amps min. and the New Bat. still drains while running only.
 

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If you are saying that the battery drains only when the car is RUNNING? then the Alternator is NOT charging and the car is running off of straight battery. Need to know that :
a. Belt is not slipping.
b. the 12 volt Exciter circuit is telling the alternator to make power.
If you have the alt tested off the car and it is good, then you need to check to see if infact the wire is transmitting a good 12 volt signal to tell the Alternator to Charge.
I do not know which wire / circuit that is off the top of my head
 

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It would be like this ↓



WHITE WIRE in drawing becoming HOT ONLY with Ign on, to EXCITE the Altenator.
 

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I dont know shinola about electric, but I would look for some insulation worn on any wire. maybe a light show in the dark.
 

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According to the schematic I have here for an '84, there is a resistance wire feeding the alternator field, as well as a GEN lamp. The resistor is there to bypass the GEN lamp if it burns out. The circuit is fed from the fuse panel section that's switched by the ignition switch. The field wire is brown at the alternator.
On the 4th gen stuff, I had GEN problems when the AC/heater fuse was out (strange).
 

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Guess I could have spelled it out, just thought the Drawing would explain the Wire hook up for the Exciter part of the Alternator as JeffsNickle9 was explaining. So here it is
Electrical - Wiring up the Alternator
NOTE: BLACK WIRE IN PHOTO IS JUST AN ADDED EXTRA GROUND I ADDED TO THE FIRE WALL, I LIKE GROUNDS, LESS ISSUES WITH BAD GROUNDS THAT WAY. But it won't be in your Harness. ***See Trouble shooting note at bottom of Page ***


GM

One of best inventions in the early 70s, is the three wire alternator. The voltage regulator is built into the alternator. This makes it very easy to wire up and it also has the added benefit that the voltage regulator is no longer a mechanical device but now semiconductor based - no adjustments!
There is a common misconception about alternators and the term one wire alternator is often thrown about. Most people mistakenly identify a 3 wire alternator as a one wire alternator (I know, I was one of those). A one wire alternator was only used for limited applications and has distinct disadvantages. The 3 wire alternator is a proven design and has been used for the past 30 years starting in the late 60s, early 70s. .

3 wires are actually used plus chassis ground



There are 3 wires needed to run it and the case provides the path to chassis ground Even though there are 3 wires, it is very easy to wire up. Here's a desorption of the wires:


  • Battery positive (Bat+)
    • connect to starter +12V battery wire
    • use 10 ga wire (thick)
    • Screw on terminal on the back of the alternator
  • Voltage sensing line
    • connect to the Bat+ close to the firewall
    • Senses and adjusts the +12V were it is needed
    • use 14 ga wire (thinner)
    • Pin 1 of the push in connector on the alternator
  • Ignition On input
    • When the ignition switch is turned on, power from the ignition switch turns on the alternator
    • Pin 2 of the push in connector on the alternator
    • use 18 ga wire
    • In the above pictures, you can see a black wire that is connected to the alternator mounting bracket. I ran an extra ground wire from the firewall directly to the alternator's mounting bracket just cause I'm paranoid about bad grounds. Normally the engine has a ground strap between it and the firewall which provides an excellent ground. I've painted all my parts and want to make it 100 percent sure. Most likely it is not needed as millions of cars work perfectly fine without it.
Between the starter and the battery is a short piece of wire about 1" long that is a smaller gauge than the main wire. It is a fusible link. The idea is that if there is a catastrophic short in the wiring harness, the fusible link will burn up before the rest of the wiring harness. It operates on the same principle as a fuse.


On internally regulated models, there are also four connections on the alternator, but there is no separate regulator in the system - it is inside the alternator and constructed of solid-state components. The connections here are the large output terminal (BAT), the ground terminal (GRD) which may be "implied" though the metal mountings of the alternator, and two connections typically labeled simply 1 and 2. Terminal #1 on an internally regulated alternator is the same as terminal #4 on the regulator of an externally regulated system - it connects to a small wire that is goes to the charge indicator light on the dashboard of the car and the charge resistance wire. Terminal #2 on an internally regulated alternator matches terminal #3 on an external regulator - it is connected to the main junction block for the wiring system and serves as a "remote voltage sensing wire". If you are comparing to the externally regulated wiring, then you will note that the F and 2/R wiring connections are done inside the alternator. A typical internally regulated alternator wiring diagram is below for reference - click on the image to see a larger view.

TROUBLE SHOOTING:

If you have a GM vehicle, (or a GM conversion) and the battery and alternator both test good, but it still will not charge, Check these three things...
1. Check the idiot light. The system won't charge reliably if the bulb is burned out or missing.
If you opted not to have a light, or your vehicle didn't come with one, check the resistor or diode just behind the alternator 2 wire plug.

2. Check the fusible link. The fusible link is a soft wire with tape or a plastic collar about 3 or 4 inches from the end.
(Plastic collar is about 3/4" inch long X 1/2 inch dia.)
The fusible link is usually found connected to the battery cable side of the starter solenoid.

3. Check to make sure the alternator is grounded. A good 85% of alternator problems are ground related.
Most factory installed alternators rely on engine ground or alternator bracket ground to service the alternator.

BAD IDEA!!
Outside of the starter, the alternator will require the largest capacity ground!
Rust on brackets, blocks or in bolt holes, painted surfaces, and loose fasteners all contribute to loosing ground capacity.
It doesn't have to be a total break in connection to cause problems or kill the voltage regulator.
The reason the factory didn't dedicate a ground wire to the alternator is $$$.
By doing a 'Close Enough' ground, they save the cost of the wire, connection ends, and labor to install it.
More to Follow ↓
 

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Batt

(Red AWG #10 or #8 wire going to insulated terminal at rear of alternator) This terminal is for the alternator output to the battery. On Land Rovers equipped with an ammeter this lead goes directly to the ammeter POS terminal. The ammeter NEG side goes to the battery positive terminal, usually by being connected to the starter switch or relay. A 10 gauge wire will work for all the 10-SI alternators and the low to mid amp 12-SI alternators. The high amp 12-SI should get a AWG #8 wire. You should install a fusible wire link in this wire in case of an accidental short to keep the shorted wire connected directly to the battery from starting a fire. The fusible link should be placed near the battery.
1 "Excite"

(White AWG # 14 or #16 wire on white molex plug) This wire provides the start up voltage for the alternator. The "1" alternator terminal is fed by a switched 12V source from the ignition switch through a lamp ("idiot light") and is used to supply the magnetic field inside the alternator with the voltage needed to operate. The alternator can not start charging until there is a voltage on the field winding and a magnetic force is created.
The “idiot” light is there to act as a visual indicator of under voltage and over voltage conditions at the battery. When the engine is running, if the idiot light is on, the output voltage of the alternator is out of specification.
2 "Sense"

(Red AWG #10 or #12 wire on white molex plug) The 'Sense' wire checks the voltage output level of the alternator. This is the reference voltage that the alternator uses to determine how much power to put out. If the sensed voltage gets higher than the regulator is adjusted for, the regulator causes the alternator to momentarily stop charging until the sensed voltage drops down to a specified amount, then the alternator resumes charging. The regulator basically turns the alternator on and off fast enough to keep the output voltage within a specified voltage range.
The Number two "sense" terminal is often connected to the BATT. terminal at the back of the alternator. This is the simplest connection and the least desirable since it is measuring the alternator output and not the voltage at the load connections. Any voltage drop due to loose, dirty or corroded connections and internal resistance of the wires and components is not accounted for and the voltage at the circuit loads may be lower than it should be. The voltage is best sampled in the interior of the vehicle after the fuse block load, where all the electrical current load of the vehicle is. The 'Sample' would better sense a voltage drain and and the alternator would correct for it.

Gnd

(Black AWG #10 or #8 wire going to screw on back case of alternator) When most people convert to a SI Series Delco alternator they leave off the ground wire and rely upon the alternator mounting bolts, engine block and engine to ground strap for an alternator return path. This works just fine most of the time as long as the mounting bolts are making a good electrical connection. Sometimes the ground connection may not be all that good or it may get worse over time. This higher resistance connection keeps the alternator from generating its full rated amperage. An AWG #10 or #8 gauge wire between the alternator ground connection and a good frame ground assures a good pathway for the alternator. This wire should have a fusible link in case your engine to frame ground strap fails and tries to route all the starter current through the alternator ground wire.

Some common fault symptoms and what they most likely indicate:

  • AM radio interference, bad rectifiers.
  • Battery discharges overnight, bad rectifiers
  • Charging voltage below 13V above 2000 engine RPM alternator likely not working. Pull alternator and take down to shop to be tested.
  • Idiot light does not come on when key on and engine not running, bad bulb or electrical connection.
  • Stop vehicle & check immediately If not belt look for a connection that just came off. Your alternator has stopped charging. If nothing obvious can be found, pull alternator and have it checked on a machine.
  • Idiot light on very dimly. Alternator charging but not enough to keep up with current drain produced by vehicle electrics.
The most common charging problems are caused by poor connections, especially poor ground connections. Be sure to check all your connections. If you are using crimp connections be sure to inspect the crimp for connector and wire oxidation.

THANK you for your Time and Patience.
 
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