GMC Battery Drain

GMC
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WILDTHING
  • MEMBER
  • 9 POSTS
When i hook up my battery,there is a larger than normal spark. My car will have starter chatter if it sits for a couple days. I want to do a power draw test.
How would I do that?
May 23, 2006 at 5:28 AM
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LOSONE
  • ✓Experienced Mechanic
  • 1,616 POSTS
Let me tell you how to find a battery drain problem.

Buy a digital voltmeter that has an Amp scale. (About $20.00)

Disconnect the negative battery lead.

Put the meter on the 10Amp scale. Put it in series with one lead on the battery and the other lead on the ground cable.

This will show you the battery drain in Amps. A perfect set up like your car should not be over 25MA (.25AMP) and that will be the radio memory. This is called the parasytic load.

I would pull the fuse for the interior lights so opening the door will not affect the meter reading.

Make a list of everything you do.

First take a reading with everything connected, record it. Next, pull the alternator wires including the big red one and take a reading. (One at a time)

Next pull each battery driven fuse one at a time and check the reading.

When the reading drops you have isolated a battery drain.

You can isolate shorts/drains in good order that way by disconnecting wires that control something. I have used this method hundreds of times so it works.

Let me know
May 23, 2006 at 7:17 AM
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Suggested Repair

Measure parasitic draw with a digital meter on the 10-amp scale in series between the negative battery post and the disconnected ground cable. Pull the interior-light fuse so opening a door does not affect the reading. Record the baseline, then disconnect the alternator wires and pull battery-fed fuses one at a time until the draw drops to isolate the circuit.

Conversation Summary

The owner of a GMC reports a larger-than-normal spark when connecting the battery and starter chatter after the vehicle sits a couple of days, and asks how to perform a power-draw test. The expert explains a parasitic-load test: place an ammeter in series on the negative battery cable, keep interior lights from affecting the reading, record a baseline, then disconnect the alternator wiring and pull fuses one at a time until the draw drops.

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