Dead Battery - How do I troubleshoot short with a Multimeter?

Platonic Solid · May 4, 2006

I hooked up my fully charged, practically new, battery and it was completely dead 8 hours later. Yesterday I ordered a new Voltage Regulator and related pigtail connector since the one that’s there looks really nasty. I would have purchased a new alternator harness, but apparently that’s not available for 73, so I just replaced the 2 spade connectors and cleaned the other connection. Since I still see a spark when I go to connect the positive battery cable to the battery, I assume the problem is still there. How do I use a Multimeter to locate the source of the power drain? Should I be measuring DC Volts, µAmps, mAmp, or Amps? Open circuit or closed circuit? Is there an easy process of elimination I should follow by removing fuses?

pabear89 · May 5, 2006

Same way as a testlight?

Remove neg batt cable connect voltmeter inbetween batt and cable,
set to read volts.
pull fuses till voltage reads 0.

Start with known draws first ie. radio feed, dome lites, ect.
PB

Platonic Solid · May 5, 2006

OK, so I was having a major senior moment. Funny how blatantly obvious it seems after someone tells you how to do it.

It wasn’t working for me cause I was trying to measure a voltage between the disconnected positive battery terminal.

Thanks much

1966conv · May 5, 2006

As a side note don't leave the doors open to make getting to the fuses easier, you'll have a drain because of that circuit being energised. Ask me about that one. (scratches head)

Your headlight switch is also a seperate circuit from the fuse panel IIRC. you may have to pull the wiring of that to see if the switch is bad.

Tim65GT · May 5, 2006

Your headlight switch is also a seperate circuit from the fuse panel IIRC. you may have to pull the wiring of that to see if the switch is bad.

Good tip.

Use the Amp setting and hook the red lead to the positive battery. Hook the negative to the disconnected positive cable.

If you have more than 1 amp with everything turned off, start pulling fuses to see if you can get it to drop.

If you have aftermarket accessories, make sure you check those. A new type of radio with memory stations should only draw a few milli-amps from the battery, thats ok.

Don't forget the light switch as mentioned above.

ForceFed70 · May 5, 2006

The best method is to actually use an ammeter.

If you pull off the battery cable and put a DVM in there it'll read 12V no matter what. It'll read 12V on a perfectly normal car.

With the ammeter you can see how much current the car is drawing. Anything more than 1/2amp with the key off is going to cause problems. Pull fuses until current drops off, then you've narrowed the problem down to a single circuit.

I would check your stereo equipment 1st...it's often the culprit.

Platonic Solid · May 6, 2006

Tim65GT said:
Use the Amp setting and hook the red lead to the positive battery. Hook the negative to the disconnected positive cable. ...

I used this method and got a reading of 2.2 Amps (which I didn't get before cause I had the probes plugged into the wrong holes on the meter ). When I unplugged the old Voltage Reg., the Amp reading dropped to "0". The new Voltage Reg. came with an instruction sheet, which includes a Resistance test to check it with (I don't know if this applies to all year VR's):

1. Bolt VR to vehicle.
2. Before plugging in harness, check resistance between the Field (F) Terminal and Ground.
2.A. If the Resistance is less than 2 Ohms, the Circuit is Shorted and Must be repaired before connecting the Regulator.
2.B. If the Resistance is more than 6 Ohms, there is a bad connection or Open Circuit which must be repaired before connecting the Regulator.

The Resistance on my new VR measures 1.9 Ohms, but seems to work fine.
The Resistance on my old VR measured 10.0 Ohms, well above the 6 Ohm test max.

Thanks All

:SNSign:

Dead Battery - How do I troubleshoot short with a Multimeter?

Platonic Solid

pabear89

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Platonic Solid

1966conv

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Tim65GT

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ForceFed70

That's why they call it "dope"

Platonic Solid

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