Battery Drains Overnight..draws Over An Amp

Discussion in 'Fox 5.0 Mustang Tech' started by foxbodymike87, May 22, 2013.

  1. Here's how to do it...

    Alternator wiring.


    Starter solenoid wiring 86-91 model cars.

    Connect the fused 4 gauge wire to the alternator and the battery side of the starter solenoid.

    Starter solenoid wiring 92-93 Model cars.
  2. Why do you think I buy my parts from Advance? Lol.

    Here is also a writeup. This is the one I found to be the easiest. That and you use fusible link wire, which I think makes it look better, and you don't have to go on the hunt for the fuse, fuse holder and all. The wire is $11 at Carquest (PN# PW12F). You can also get it off Ebay for half the price, just unsure cost of shipping, if there is any. This write up is straight forward, no way to mess it up.

    Not trying to steel your thunder or take away your post jrichker :)
  4. Yep, I buy lots of stuff online from them, usually with at least a 20% off code. They also price match other vendors- I scored a $60 set of brake pads for $30 and a set of $75 rotors for $28 recently.

    The only issue I have with that 3g writeup is he cut the original power wires, which I do not recommend. You simply tap into the stator wire and wrap the 2g power connector up and tuck it away.

    I bought the 4g power wire off a buddy on the Corral. It is the nicest setup I've seen and is cheaper than sourcing the parts yourself. Even includes the bolt for the alernator.

    View attachment 128654
  5. Ok, put in the new alternator..and the store tested it and it was good..but when its running the battery is at 11v so the alt isnt charging and its still pulling almost an amp of current.
  6. Check the stator wire connector and the voltage output at the back of the alternator.
  7. What do i prong?
  8. Alternator troubleshooting for 86-93 5.0 Mustangs:

    Never, never disconnect an alternator from the battery with the engine running. The resulting voltage spike can damage the car's electronics including the alternator.

    Revised 15 April 2012 to add simple check for regulator failure in Engine off ignition on, battery fully charged section, item 2.

    Red color text applies to cars with a 3G alternator.

    Do all of these tests in sequence. Do not skip around. The results of each test depend on the results of the previous tests for correct interpretation.

    Simple first step: Remove the alternator and take it to your local auto parts store. They can bench test it for free.

    Engine off, ignition off, battery fully charged.
    1.) Look for 12 volts at the alternator output. No 12 volts and the dark green fuse link between the orange/black wires and the battery side of the starter solenoid has open circuited.
    3G alternator: Look for 12 volts at the stud on the back of the alternator where the 4 gauge power feed wire is bolted.
    No voltage and the fuse for the 4 gauge power feed wire is open or there are some loose connections.

    2.) Look for 12 volts on the yellow/white wire that is the power feed to the regulator. No 12 volts, and the fuse link for the yellow/white wire has open circuited.

    Engine off, ignition on, battery fully charged:
    1.) Alternator warning light should glow. No glow, bulb has burned out or there is a break in the wiring between the regulator plug and the dash. The warning light supplies an exciter voltage that tells the regulator to turn on. There is a 500 ohm resistor in parallel with the warning light so that if the bulb burns out, the regulator still gets the exciter voltage.
    Disconnect the D connector with the 3 wires (yellow/white, white/black and green/red) from the voltage regulator.
    Measure the voltage on the Lt green/red wire. It should be 12 volts. No 12 volts and the wire is broken, or the 500 ohm resistor and dash indicator lamp are bad. If the 12 volts is missing, replace the warning lamp. If after replacing the warning lamp, the test fails again, the wiring between the warning lamp and the alternator is faulty. The warning lamp circuit is part of the instrument panel and contains some connectors that may cause problems.

    2.) Reconnect the D plug to the alternator
    Probe the green/red wire from the rear of the connector and use the battery negative post as a ground. You should see 2.4-2.6 volts. No voltage and the previous tests passed, you have a failed voltage regulator. This is an actual measurement taken from a car with a working electrical system. If you see full or almost full12 volts, the regulator has failed.

    Engine on, Ignition on, battery fully charged:
    Probe the green/red wire from the rear of the connector and use the battery negative post as a ground. You should see battery voltage minus .25 to 1.0 volt. If the battery measured across the battery is 15.25 volts, you should see 14.50 volts

    Familiarize yourself with the following application note from Fluke: See for help for help troubleshooting voltage drops across connections and components. .

    You will need to do some voltage drop testing of several of the wires.

    Start looking for these things:
    1.) Bad diode(s) in the alternator - one or more diodes have open circuited and are causing the voltage to drop off as load increases. Remove the alternator and bench test it to confirm or deny this as being the problem.

    2.) The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Do the voltage drop test as shown in the Fluke tech note link. Measure the voltage drop between the alternator frame and the battery negative post. Watch for an increase in drop as the load increases. Use the Fluke voltage drop figures as guidelines for your decisions.

    3.) Bad regulator that does not increase field current as load increases. Remove the alternator and bench test it to confirm or deny this as being the problem.

    4.) Bad sense wire - open circuit in sense wiring or high resistance. The yellow/white wire is the voltage sense and power for the field. There is a fuse link embedded in the wiring where it connects to the black/orange wiring that can open up and cause problems. Disconnect the battery negative cable from the battery: this will keep you from making sparks when you do the next step. Then disconnect the yellow/white wire at the alternator and the green fuse link at the starter solenoid/starter relay. Measure the resistance between the alternator end of the yellow/white wire and the green fuse link: you should see less than 1 ohm. Reconnect all the wires when you have completed this step.

    5.) Bad power feed wiring from the alternator. Use caution in the next step, since you will need to do it with everything powered up and the engine running. You are going to do the Fluke voltage drop tests on the power feed wiring, fuse links and associated parts. Connect one DMM lead to the battery side of the starter solenoid/starter relay. Carefully probe the backside of the black/orange wire connector where it plugs into the alternator. With the engine off, you should see very little voltage. Start the engine and increase the load on the electrical system. Watch for an increase in drop as the load increases. Use the Fluke voltage drop figures as guidelines for your decisions.


    Alternator wiring circuit
    Notice the green wire connects to a switched power source. The circuit contains a 500 ohm resistor in series between the switched power and the alternator. Connecting it to switched power keeps the regulator from drawing current when the engine is not running. The resistor limits the current flowing through the wire so that a fuse isn't needed if the wire shorts to ground.

    Also notice the sense wire connects to the starter solenoid and it is fused. It connects to the starter solenoid so that it can "sense" the voltage drop across the output wiring from the alternator.
  9. Stator wire is the male 1 wire connector on its own to the back of the alternator.

    do what jrichker says regarding the checklist. You want to see the same voltage at the alt power post as the + battery terminal with the key off. You need at least 12.7 volts to start the car. With the car running and the alternator charging, you should see about the same volts at the power post on the back of the alt as the + battery terminal.

    As discussed before, unless you are using a dedicated 4 gauge power feed with at least a 125 amp megagfuse inline and a another 4 gauge ground wire, you are asking for problems. The stock wiring is not designed to handle an upgraded alternator.
  10. I dont know if this means anything but with the alternator disconnected i am still pulling over an amp
  11. It means that the alternator is not your problem. Keep on lOOking...
  12. Pull out each fuse one by one and see if that stops the draw. Where are you checking the amperage draw, at the alternator connections? If so, start there and work your way back to the starter solenoid and battery. Not to send you on a goose chase, it could be a hundred places but your starter/connections could be the cuplrit. Does it start easily?
  13. Next on my list of things to check after verifying all grounds and connections are good would be the starter.
  14. Starts nice and fast with a full pulling the amps from the battery..
  15. I just pulled amps again with everything connected and now there isnt any draw...pulling 0 amps...
  16. I'd be looking for the remains of an aftermarket alarm, aftermarket lights, aftermarket stereo. It's EASY to wire those up without even putting power through the fuse block, meaning you can pull all the fuses out of the fuse block and still have a draw you haven't found. I chased my tail for months looking for the source of a drain and found out it was a relay for aftermarket driving lights that some dip:poo: [cough] ME [cough] had wired up improperly years before. I accidentally reversed the power and switched terminals and it made for a constant drain. I'm not saying that specifically is your problem, just to point out that you have to be aware of every electrical component or remnant in the car before you'll have any success chasing anything like this down.'s your ignition switch?
  17. You aren't checking for a drain with the door open are you? Anyhow..I fought one in my car. Intermittent. The glove box light switch was the culprit. Another thing, if it is there intermittently meaning only sometimes when you test it does it pull an amp, it could be a relay contact sticking. Try pulling relays too while watching your meter. Anything in the car acting weird or not working? And your amp draw should be under .5 amps.
  18. Well now everythings connected and the battery isnt draining and im pulling 0 amps

    So idk..i didnt do anything different but the alt still isnt charging the battery