Help Diagnose My Parasitic Battery Draw

General Truck Discussion Electrical & Wiring
1

Having trouble with a battery that keeps going dead? Post your details here and we’ll help narrow it down.

Include as much of this info as you can:

Truck info:

  • Year / make / model:

  • Engine:

  • Battery age:

  • Alternator age / charging voltage:

  • Any recent electrical work, stereo, alarm, lights, trailer wiring, remote start, etc.:

Symptoms:

  • How long does it take for the battery to go dead?

  • Does it happen overnight, over a few days, or only after sitting longer?

  • Does it still crank slow after a full charge?

  • Any warning lights or weird electrical issues?

Testing done so far:

  • Battery voltage after sitting:

  • Charging voltage while running:

  • Parasitic draw reading, if checked:

  • Fuse pulls tested:

  • Anything that wakes up randomly, clicks, hums, or stays lit:

Common things to check on GMT400, GMT800, GMT900, and K2XX trucks include glove box lights, underhood lights, aftermarket stereos, OnStar/modules staying awake, trailer brake wiring, door switches, cluster issues, BCM problems, and corroded grounds or battery cables.

Post your results below and include photos or meter readings if you have them.

2

We just published a full guide and video on diagnosing parasitic battery draws across GMT400, GMT800, GMT900, and K2XX trucks — covering letting your modules go to sleep before testing, pulling fuses one at a time, checking for failed alternator diodes, and known issues like GMT800/900 instrument clusters and K2XX door harness pinch points.

Read it here: How to Find a Parasitic Battery Draw on GMT400, GMT800, GMT900 & K2XX - FullSizeChevy.com

If you’re fighting a draw, fill out the template in the post above and reply here with your details — year/make/model, engine, platform, battery age, alternator test result, measured draw, fuse that drops the draw, aftermarket accessories, and recent repairs. Photos of your battery wiring and fuse panel help a lot too.

A few things worth checking first:

  1. Did you let the truck fully go to sleep (doors closed, key out, 30-40 min) before measuring? A lot of “huge draws” are just modules that haven’t timed out yet.
  2. Pulled the fuse for any aftermarket remote starter or alarm?
  3. Checked both the underhood AND interior fuse panels?
  4. Tested whether disconnecting the alternator’s main lead drops the draw (possible bad diode)?
  5. Got a trailer harness or hitch-mounted brake controller? Corroded trailer plugs are an easy thing to overlook.

Post your results below and let’s get these batteries sorted out.