'85 Battery Drain
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'85 Battery Drain
Something keeps draining the battery on my 1985 F150. It has the 5.0 EFI engine. Once charged it will provide enough juice to use the vehicle during the day, but goes dead over night. I have tried 3 different batteries with the same results so I know that is not the problem. Is there a systematic way to try to trace this problem or is it a trial and error crap shoot?
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Joined: Dec 2004
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From: Connecticut
Here's how to track down an electrical drain:
1.) remove one of your battery cables (doesn't matter which one)
2.) get a multimeter and set it to Volts DC
3.) attach one lead to the battery post
4.) attach the other lead to the battery clamp
5.) with the ignition switch OFF, it should show 0 volts (open circuit)
6.) if you get a voltage reading (positive or negative), something is drawing power
7.) start pulling fuses until the voltage goes to 0 volts, this will tell you which circuit is causing problems
1.) remove one of your battery cables (doesn't matter which one)
2.) get a multimeter and set it to Volts DC
3.) attach one lead to the battery post
4.) attach the other lead to the battery clamp
5.) with the ignition switch OFF, it should show 0 volts (open circuit)
6.) if you get a voltage reading (positive or negative), something is drawing power
7.) start pulling fuses until the voltage goes to 0 volts, this will tell you which circuit is causing problems
Senior User
Joined: Oct 2005
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My 85 did the same thing and i tried the trick with the multimeter and when i unpluged the volts regulator it went to 0 volts then i went and purchased a new volts regulator from a local alternator shop for about $20.00 after i installed it i havent had a problem yet the volt regulator is a square box mounted right close the battery and starter solenoid i have a picture here.
Postmaster
Joined: May 2004
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A fairly common problem that also causes a drain, and therefore a voltage reading, is a bad diode in the alternator. You can test for that by disconnecting the line from the positive terminal to the alternator. If voltage goes to zero, you got it....replace the alternator. Good luck.
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I Have A 1986 F150 Xlt That Has A Slow Battery Drain Problem . But If I Crank It Daily And Drive It Doesnt Go Down. This Mornig Battery Was Dead So I Jumped It Off It Cranked Up For About A Minute Or Two And It Died Now Wont Start Anyone Can Sugest Any Sollutions
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Get a testlight and hook it up like the diagram below. If it glows bright, you do have a drain. Once you get it hooked up, and the testlight is glowing bright, start pulling fuses one at a time out of the fuse box. Make sure the domelight is off when you do your test, or it will cause a drain and give false results. When you come across the fuse that makes the light go out, then you know what circuit is causing the drain.
If none of the fuses makes the light go out, then pull all the wires off the alternator. If thel light goes out, then you know you have a faulty diode in the alternator.
P.S. A voltmeter does not work very well unless it's a very cheap one. A good voltmeter is too sensitive and will pick up the small drain from the memory circuits in the radio, and other small normal drains.
If none of the fuses makes the light go out, then pull all the wires off the alternator. If thel light goes out, then you know you have a faulty diode in the alternator.
P.S. A voltmeter does not work very well unless it's a very cheap one. A good voltmeter is too sensitive and will pick up the small drain from the memory circuits in the radio, and other small normal drains.
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