Electrical Battery Discharging, 92 Lx 5.0

Discussion in 'Fox 5.0 Mustang Tech' started by KW_Pilot, Oct 9, 2013.

  1. My battery is discharging to the point where I need to start the car every few days. I just bought the quick disconnect from Late Model Resto and disconnected the negative for 6 days while on vacation. The car started but the battery light remained on for about 20 minutes after starting, showing it's still having a good amount of drain even disconnected. The battery is brand new and is a AutoCraft Gold series from Advance.

    Anyone have any ideas?
  2. Typically it is something draining the battery. Small things like glove box or courtesy lights are often the culprits. If you have an aftermarket stereo or alarm system, it is also suspect.

    The ideal method is to disconnect the negative terminal, and connect a Digital Multimeter (DVM) between the negative terminal on the battery and the negative cable. Set the DVM on a low current scale of 2-5 amps if it doesn't auto range. Watch the current draw, and then start pulling out fuses. When you see a sudden drop in the current, that circuit is the likely culprit. Note that the computer, radio & clock will draw less than 1/10 amp to keep the settings alive.

    Using the negative side prevents nasty accidents like shorting the wrench to ground while disconnecting the battery cable. Electrically, the test will work with either positive or negative battery cable.
  3. Thanks man, I'll give it a try this weekend.
  4. Just to add one item to jrichker's list of common culprits that can drive you nuts is the under hood light, the switch fails in the "on" position.
  5. And if you have ANY aftermarket lighting or stereo equipment, you need to check the wiring and relays for those, because they may not be running through the factory fuse block, and doing amp-drop testing pulling fuses won't find the culprit.
  6. Just wondering if you ever found the culprit I'm dealing with a similar problem on my 92
  7. Earlier this year I had that and it turned out my hatch was just slightly ajar and my "trunk" light was on. I rarely open my hatch, and after about one week of my battery dying "for no reason" I asked myself what was different than before. I then remembered I got something out of my trunk the week before and voila! problem solved. Hopefully yours is this easy.

  8. I'm still on the search for my electrical issue. For now, I just ensure I start the car every few days.
  9. A new battery drained with the negative cable removed from the battery terminal? Only possibilities: battery is bad, alternator is not charging it fully.
    Grabbin' Asphalt likes this.
  10. I would take the car over to a Super Wal-Mart that has a Tire Lube Express or Autozone and let them hook a tester up to the battery. It will test your Battery, Alternator, and Starter. If the battery is bad it will say bad cell. If the alternator is bad, it will more than likely be an open diode inside the alternator. If your disconnecting the NEG battery cable and its still draining then it has to be the battery. Just cause things are new doesnt always mean they are good. If your leaving it connected then jrichker gave some really good advice.
  11. Just wanted to update since I found my parasitic battery drain, only took a few days after dealing with it for several years. I used a test light between the positive lead and the positive terminal on the battery and began pulling fuses until the light went out. The culprit was a 15 amp fuse that was stuck in "spot 7 spare" once I pulled it out the light went out problem solved. I couldn't have done it without suggestions from this site.
  12. the dreaded spare fuse ;)
  13. I have a similar problem. My car some times sits for a week or longer before I get time to take it out. I know I dident fix the problem but I found a way that the battery wouldent drain. When ever I park my car for longer than a day I pull my inline fuse under the hood that powers my amps. Whenever I have time I try to track it down using a voltmeter. I hate tracking down electrical problems
  14. You have already found the source of your problem. The amplifiers are wired into circuit that does not turn power off when you turn the ignition switch off. They may have tied the amplifier internal on/off circuit to the same continuous DC power circuit that supplies power to the amplifier when it is being used. Not all amplifiers have this internal power control feature. Some amplifiers may require that the main amp power run through a high current relay that turns on when the ignition switch is in the Accessory or Run position.