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Thread: Parasitic battery drain/help me play Perry Mason.....

  1. #1
    I post a lot... Toploader's Avatar
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    Default Parasitic battery drain/help me play Perry Mason.....

    Ok on my '86 Tudor GM 5.0 Several months ago I put in a new battery, all was good for several months. Then all of a sudden I come out one day and DEAD........I mean not even the 'ol click-click-click! Ok call AAA and get a boost car starts immediately, I let her run for about one hour....shut her down....come back the next day starts right up. Then I leave the car for one week..come back...you guessed it....DEAD battery. Call AAA again, they come, boost car, starts right up....run for one hour, shut down...come back the next day starts right up....wait three more days...starts right up. Then she sits again for about a week and a half...you guessed it DEAD. Ok so this has happened four times. I assume I have a parasitic drain someplace, but where to look?....the interior lights were never left on, there is no bulbs under the hood or trunk, I removed the glove box bulb. I know the ALT works because I see the headlamps get brighter when I feed gas. My bud told me to remove the negative battery cable then come back days later. Can anyone explain why he said I should do that? This is battery drain 101 for dummies. What could be draining the battery???
    Last edited by Toploader; 03-18-2021 at 01:02 AM.

  2. #2
    Wagon Addicted Tiggie's Avatar
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    An hour of the car running, especially at idle, is likely not sufficient to fully charge the battery.

    With the key off, Put a multimeter between the battery negative and the disconnected negative terminal. Should be less than 100 milliamps. If more, you can pull a fuse to isolate the problem circuit. I'd start with the the radio circuit.
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  3. #3
    Member WagonMan's Avatar
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    I have seen this twice with box body cars. The rear defroster switch goes bad and keeps the defroster on and kills the battery, even with the key in the off position. WagonMan
    1990 Colony Park
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  4. #4

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    Radio, computer, etc are always there so unlikely to be causing new problems. Alternator can develop an internal short circuit.

    I had the same problem a couple days ago: my fairly new battery had a bad cell, it would charge to 13.2 volts but the tiniest draw would almost instantly bring it down below 10. It was still under the full warranty so I got a new one for free.

    My initial thought was that the battery was being drained by something, but it was an internal failure.

    If it's nothing obvious like that, get a good old fashioned test light, and a hose clamp. Pull the negative cable off the battery, clamp the pointy end of the light to the battery terminal, and clip the alligator clip to ground. Then pull fuses one by one and see if the light goes out. If not, start removing wires from the starter solenoid. There will probably be a few (radio, computer) that glow dim but any draw big enough to drain the battery overnight will be bright enough to see clearly from the driver's seat as you pull the fuses.

  5. #5
    Beater gonna beat sly's Avatar
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    +1 alternator can pull less than 1 amp when the car is off in certain failure modes. This is why I bought the clamp meter I have, just to diagnose this specific issue. I've seen 3 or 4 alternators die like this so far between my own cars (1) and people from church and friends (the rest). I prefer the inductive sensing of a clamp meter rather than disconnecting the charge cable from the alternator and putting a current meter across the gap.

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  6. #6
    I post a lot... Toploader's Avatar
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    Thank you gents...for the time being I pulled the neg cable off of the battery as I will not need t move the car for one more week....if I put the cable back on and the battery is dead...well that tells me battery is n/g...if not I will hook up meters a suggested here. Also would never even thought about the rear def grid switch, thanks!

  7. #7

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    I'm with you on the clamp meter, Sly, but for those who don't have one, a test light (or a spare socket, bulb, and a bit of wire) is usually easy to find in the spare parts bin or the cheap auto parts shelf; and if you're working alone, it's easy to set up so you can see it between the cowl and the hood while you're in the driver's seat pulling fuses.
    But if it's a job you have to do twice, or you don't want to reset all the radio presets and clock and stuff...the clamp meter is better.
    I avoid a "proper" inline amp meter as most of them blow fuses above a few amps; bump the headlight switch or turn the key a smidgen too far or forget that the stereo is on, and the meter fuse (or the meter itself) lets the smoke out.

  8. #8
    Beater gonna beat sly's Avatar
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    Ditto on avoiding amp meters because blowing the fuse in them.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
    Quote Originally Posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
    Quote Originally Posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

  9. #9
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    I am happy with this slightly expensive clamp meter. Klein CL800. It is like the swiss army knife of multimiters. It has AC/DC inductive amp readings, (many are only AC) DC down to 10Mma. It also has the LowZ volt function which can be really helpful these days when ringing out household wiring. Plus many other features. I used the capacitance function to diagnose my air compressor starting issue. Even a NC volt sensor. By shopping around you can sometimes find slightly better deals than this. Caution... It is made in China.

    https://www.amazon.com/Auto-Ranging-...6249831&sr=8-6
    Last edited by jaywish; 03-20-2021 at 10:31 AM.
    "X" car 89 Colony Park LS Mods>Engine delete, SS duals magnaflow hflow cats, 2010 Must GT mufflers, auto air shocks, Posi, Tran cooler, big front brakes, 03+ rear disks, Large 3g alt, Tripminder, GS grill, 86 seats, 16" HPP wheels, winter boots=96 Cartier wheels, 215-65/16 Goodyear ULTRA GW3 snows, pi rear sway, alum driveshaft.
    03 Marauder DBP, HS, 6disk, Organizer, Silver Stars, M&Z rear control arms, Oil deflector.
    02 SL500 Silver Arrow
    08 TC Signature Limited, HID's Mods>235/55-17 Z rated Cooper Zeon RS3-A, Addco 1" rear Sway, Posi, Compustar Remote Start, floor liners, trunk organizer, Winter=05 Mustang GT rims, Nokian Hakkapeliitta R-2 235/55-17

  10. #10
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    The only thing that I don't like about this meter, other than the China thing, is the leads plug into to bottom of the unit. I prefer the top side sockets with 90deg connectors but it is only a minor annoyance.
    "X" car 89 Colony Park LS Mods>Engine delete, SS duals magnaflow hflow cats, 2010 Must GT mufflers, auto air shocks, Posi, Tran cooler, big front brakes, 03+ rear disks, Large 3g alt, Tripminder, GS grill, 86 seats, 16" HPP wheels, winter boots=96 Cartier wheels, 215-65/16 Goodyear ULTRA GW3 snows, pi rear sway, alum driveshaft.
    03 Marauder DBP, HS, 6disk, Organizer, Silver Stars, M&Z rear control arms, Oil deflector.
    02 SL500 Silver Arrow
    08 TC Signature Limited, HID's Mods>235/55-17 Z rated Cooper Zeon RS3-A, Addco 1" rear Sway, Posi, Compustar Remote Start, floor liners, trunk organizer, Winter=05 Mustang GT rims, Nokian Hakkapeliitta R-2 235/55-17

  11. #11
    Beater gonna beat sly's Avatar
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    That's why I like my Extech MA220. Not available on Amazon right now (got mine at Frys actually). Can't find it any more since it's been discontinued. It's also made in China, but it works.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
    Quote Originally Posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
    Quote Originally Posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

  12. #12
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    This fluke looks nice. On sale for $160 It has low-z Not as nearly as feature rich as the Klein but it does have top sockets.

    https://www.tooltopia.com/Fluke-FLU1...ource=hs_email
    "X" car 89 Colony Park LS Mods>Engine delete, SS duals magnaflow hflow cats, 2010 Must GT mufflers, auto air shocks, Posi, Tran cooler, big front brakes, 03+ rear disks, Large 3g alt, Tripminder, GS grill, 86 seats, 16" HPP wheels, winter boots=96 Cartier wheels, 215-65/16 Goodyear ULTRA GW3 snows, pi rear sway, alum driveshaft.
    03 Marauder DBP, HS, 6disk, Organizer, Silver Stars, M&Z rear control arms, Oil deflector.
    02 SL500 Silver Arrow
    08 TC Signature Limited, HID's Mods>235/55-17 Z rated Cooper Zeon RS3-A, Addco 1" rear Sway, Posi, Compustar Remote Start, floor liners, trunk organizer, Winter=05 Mustang GT rims, Nokian Hakkapeliitta R-2 235/55-17

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