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voltage draw

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by tmanofcali, Jun 13, 2001.

  1. tmanofcali

    tmanofcali 1/2 ton status

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    what is the best way to track down a short? something on my truck keeps draining my battery, and i need to know the easiest way to track it down. anyone have any helpful hints or suggestions? thanks for your help......tmanofcali www.softcom.net/users/tmanofcali
     
  2. travis

    travis 1/2 ton status

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    One of the most common cuases is the voltage regulator. The best way I've found to isolate battery drains is to hook a current meter (ammeter) between the negative cable and the battery. This causes all current to flow through the meter. Do not turn on any accessories or attempt to start the motor. This will cause too much current flow and possibly damage the meter or blow the fuse if protected. All you are interested in is any current flow with the key in the off position. This is what is causing the drain. Start unpluggging things one at a time until the current flow stops. You've then narrowed down the cause. Most likely you will find the problem in the regulator/alternator circuit.

    Another possibilty is just a bad battery. Bad batteries will loose charge just sitting overnight. Pull it out and take it to your friendly parts store and have them check it.

    Hope this helps.
    Travis
     
  3. Roostr84

    Roostr84 1/2 ton status

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    Has anything electrical been added on to your rig, if so check them as well. Sometimes guys run wires direct for stereos and what not, that was the problem with mine. otherwise the multimeter battery connection is the best way.

    Chris =)
    http:// www.roostr84.coloradok5.com
     
  4. Ryan_B

    Ryan_B Registered Member

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    A voltmeter in series between the negative battery cable and the negative post, (with the cable disconnected and the voltmeter in between) will work also.

    I'd check the alternator first! Pull the plastic connector out of the alternator... See if that fixes it first. That was my source of Key off drain on my blazer.

    If thats not it...
    I'd start pulling fuses until the drain goes away. Don't disconnect anything, just pull the fuses! After you narrow it down to which fuse it is, then you get to figure out what circuits are on that fuse. Then you can narrow it down to where the short is.
     
  5. tmanofcali

    tmanofcali 1/2 ton status

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    thanks for the suggestions guys.....my alt. is newly rebuiltand the battery i just bought it 2 weeks ago. it drained once and then i had them check it and it was way low, so they recharged it for me and 2 days later....nothing. i have added a digital dash and fuel injection, but no stereo yet. my friend and i are thinking its the fuel injection computer maybe. voltage regulator is pretty new (1 1/2 years old), so i doubt its that. we will check it out this weekend and ill let you guys know the outcome. thanks again.
     
  6. Steve_Chin

    Steve_Chin 1/2 ton status

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    Check the alternator again. I had a "new" alternator in one car that drained the battery. It had a shorted rectifier diode in it that was causing the drain.
     
  7. Ryan_B

    Ryan_B Registered Member

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    Hey guys...
    I might add, if you have an alarm- if you think about i, that is only activated when the vehicle is parked so that is a potential source of Key off drain.

    Fuel injection has circuits that operate with the key off.
    Mem
     
  8. Ryan_B

    Ryan_B Registered Member

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    Hey guys...
    I might add, if you have an alarm- if you think about it, the alarm system is only activated when the vehicle is parked so that is a potential source of Key off drain.

    Fuel injection has circuits that operate with the key off.
    Memory circuits...in the ECM, and possibly Stereo, Clock, Digital Gauges...etc.
    My 2 cents.
     
  9. Steve_Chin

    Steve_Chin 1/2 ton status

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    Also with an EFI system, if the oil pressure safety cut-off switch is bad (shorted), the fuel pump will not shut off when you turn the ignition off. Found that out the hard way with a TPI car (dead battery one morning).
     
  10. big79209

    big79209 Registered Member

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    hey ryan_b im the friend that tman is talking about that will be looking at his wiring this weekend, you mentioned using a volt meter to find the source, what should the reading be on the volt meter?
     
  11. Ryan_B

    Ryan_B Registered Member

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    If you unhook the negative cable and connect the voltmeter in between the neg. battery post and neg. cable,
    The reading should be 0. (with the key off!)
    This is the case with my 1 wire alternator.
    I had a 3 wire alternator and it seemed to be drawing 4 volts with the key off. A new alternator solved this problem.
    I think the problem was a bad diode in the alternator.

    The way I found out that the alternator was draining the battery was to unhook the plastic connector clip, and then all of a sudden the voltmeter dropped to zero.

    However, for some reason on my dad's 77 Chevy truck his 3 wire alternator is drawing 8 volts while the key is off.... But the battery never goes dead for some reason.??? IT doesn't seem right. The field coil in the alternator shouldn't be getting power until the key is turned on.
    Can anyone help?
     
  12. Ryan_B

    Ryan_B Registered Member

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    IF you suspect the charging system is at fault, theres a test you can do without disconnecting a thing. Just a voltmeter to the battery.

    This test is a Load/No Load Test ... aka "Toyota Test"

    1.Read base battery voltage with key off (for example 12.6 volts)

    2.Start engine and check battery voltage with engine @ 2000 RPM's and make sure all electrical loads are off... All the lights, electric fans OFF... etc. (Voltage should increase, but no more than 2 volts from base voltage ...example, no higher than 14.6 volts)
    IF it is higher than 2 volts above base, voltage regulator is bad.

    3. Now turn on all electrical loads... electric fan, lights, heater, radio... etc. And check voltage @ 2000 RPM's
    The reading should be somewhere between the two previous readings, BUT AT LEAST .5 volt above base voltage (example: at least 13.1 volts) This makes sure the alternator can meet the needs of all the electrical loads in the vehicle, and still have a half a volt (.5 v) left over to charge the battery.

    If your last reading is not at least .5 volt above base voltage, then you have too many electrical loads for the alternator to support and still charge the battery. IT would probally be wise to get a higher amperage output alternator.

    My 2 cents ...Hope this helps
     
  13. tmanofcali

    tmanofcali 1/2 ton status

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    ok ryan, i hooked up the voltmeter with the positive lead to the wire and the negative lead to the post of the battery, the reading on the voltmeter said 13.11 volts which is what it was after charging it up from the auto store. we did the alternator test by hooking up the voltmeter and checking the base volts to the volts when the truck is running, it only jumps from the base of 13.11 to 13.85 tops? is that right? i have also pulled all the fuses including the non-fused wires that come off the fuse block. the voltage of 13.11 never changed. i have also pulled the plastic plug off the alternator and also pulled the plug off the voltage regulator, still nothing......if anyone has any thoughts or comments that would help that would be great!!!
    thanks all!!
     
  14. Ryan_B

    Ryan_B Registered Member

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    If the battery voltage increases from the base voltage of 13.11 to 13.85 (at 2000RPM's at least right?!) That's okay.
    What about when you turn on all the electrical acessories and put a load on the battery+alternator? It should be at least 13.6.

    If you disconnect the - battery cable, and hook up the voltmeter in series, (in your reply it sounded like you did not disconnect the - cable.) and if you get a reading of the battery voltage (with the key off, and all electrical accessories off) then it sounds like you have a short to ground somewhere. possibly something isn't wired up right

    Sounds like al pain in the ass... Good luck.
     
  15. tmanofcali

    tmanofcali 1/2 ton status

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    hey all....i think we tracked it down to a relay thats under the dash......i dont know what it controls, but we noticed when we hooked up the battery that it make one click, which should be opening the circut. i was wondering if anyone knows what the relay is for. it is located on the upper right hand side of the fuse block. it has a metal case with a tab that inserts into a hole and a screw that holds it on the top. it has a 3 wire plug on it. if anyone knows what this is please let me know. truck runs fine without it plugged in so it must be something extra. thanks for all the replies, they were very helpful.
     
  16. 72GMCJIMMY

    72GMCJIMMY 1/2 ton status

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    I think you may be referring to the horn relay. Does your horn work? If not your short may be in the steering column.
     

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