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Honda Accord Parasitic Draw Testing

Q. Hello Mr. Ciulla, I have a 1987 Honda Accord LXi, manual transmission, with 175,000 miles. Four months after replacing a faulty alternator, my battery light came on, again, half a mile from home. The next day my battery was dead. After replacing the battery, I started the engine and measured the voltage across the battery terminals at 16 Volts, rising to 18 Volts when I revved the engine.

Honda Accord Parasitic Draw Testing

The next day, my battery was dead, again.

When I disconnected the battery, I measured 3k ohms across the battery leads! The ignition switch was off and the doors were closed. To diagnose the continuity problem, I pulled various fuses and found that I need to remove the following fuses to bring the resistance less than 3 Megohms. Typical:

  • #21 - Battery, alternator, ignition
  • #11 - Power to PGM-FI ECU, radio
  • #14 - Cooling fan timer unit
  • # 5 - Headlight retractor control unit

I have replaced the alternator, again, but do not want to start the engine until I fix the electrical problem. I get similar resistance readings. Each time a fuse is pulled, the resistance can take 15 to 30 seconds before settling down. Does this mean there is a small wire short somewhere?

  1. What is your advice for an electrical problem like this?
  2. Why would the resistance take so long to settle down. Sometimes rising and then falling back down.
  3. Is it more likely that a bad alternator caused the electrical problems, or could the electrical problem have caused the alternator to fail?

Thank you for any advice, because I need to decide to re-register the car and spend money to fix it or just let it rest in peace at a junkyard.

Sincerely,
Mike
San Jose, CA

A.

It's possible the voltage regulator inside the alternator is bad. Here is how you test it.
  1. Connect ammeter and voltmeter.
  2. With engine running, insert short screwdriver through brush holder screw opening in rear of alternator.
  3. While touching brush holder screw, ground screwdriver against alternator cover, and note amperage readings at various speeds. Ground brush holder screw for as short a time as possible. Do not allow system voltage to exceed 19 volts as electrical system components may be damaged.
  4. Compare current output with specifications, noting the following:

    • If output is not within specifications and 12 volts is available at the alternator black/yellow wire terminal, alternator is defective.
    • If output is within specifications when brush holder screw is grounded, regulator and 12 volts is available at the alternator black/yellow wire terminal, voltage regulator is defective.
Honda Accord Parasitic Draw Testing

If the alternator and regulator check out good, then you will need to do a battery load test to be sure it is good. You need to be sure the charging system is in good working order before doing any current draw testing.

Parasitic Draw Test

Honda Accord Parasitic Draw Testing

Honda Accord Parasitic Draw Testing

Honda Accord Parasitic Draw Testing

Additional Information provided courtesy of AllDATA

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