Battery drain issue

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demon322

demon322

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Having trouble with my battery discharging in between uses. If I unhook the battery it holds voltage for over a week. If I leave it hooked up it seems to lose around half a volt a day. I assume something is pulling juice while the car isn’t running. Is there a common issue or a few typical places to check? Car is a 71 demon with stock wiring other than the ammeter bypass.

Thanks.
 
Bad diode in alternator? Would be one of the few live circuits that would draw a battery.
 
Pull all the fuses, check it for a loss, if none, put the fuses in a few at a time and pin point the loss.
Yes a alternator diode will kill a battery.

My wife's toy does the same thing, will kill a fresh battery in 2 days, I put a battery shut off switch where it is easy accessible in the interior.

The aftermarket radio in her toy kills the battery.
 
Tooljunkie said:
Bad diode in alternator? Would be one of the few live circuits that would draw a battery.
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I hadn’t thought of that actually. I did verify it was charging when running but wasn’t aware of this diode issue.

Actually. The alternator hasn’t been replaced in my 12+ years of ownership and who knows how long before then. A replacement is probably a good idea.
 
Do the same as you did with the battery. Disconnect battery,then alternator,isolate the big wire.start car the shut it off and leave battery connected.
Reason i suggested start car, some faults wont return if its not started.
Have seen alternators do this,under different circumstances.
And in some cases the fault disappears after a battery disconnect.
 
I use this and put my amp meter in place of the fuse. After a drive i proceed with testing. Never actually disconnecting battery, as my multi-meter jumps fuse before opening big circuit.
CB08613C-8B8F-43B4-B469-146A55327ABA.png
 
Tooljunkie said:
Do the same as you did with the battery. Disconnect battery,then alternator,isolate the big wire.start car the shut it off and leave battery connected.
Reason i suggested start car, some faults wont return if its not started.
Have seen alternators do this,under different circumstances.
And in some cases the fault disappears after a battery disconnect.
Click to expand...
Nice. This seems easy enough to test. I’ll give that a shot in the morning.
 
demon322 said:
Cool idea! I may have to look into this also depending on what I find out. Thanks again.
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i have done work with alternators over the years and you NEVER run an alternator with the output wire disconnected.that being said you still can test the drain from alternator by simply disconnecting the output wire and see if the battery stays up over a couple days.Do not start engine with output wire disconnected.I am betting your problem is the diodes in the alternator
 
Never ever saw any problem running with an alternator output disconnected. Make it easy,disconnect the inputs too.
Start. Stop. I didnt say run it round the block.
 
You should not need to run the engine with the alternator disconnected. Having said that you an just pull the field wires as well

If the drain is alternator connected, simply disconnecting the output wire with engine stopped should show up as reduced battery drain.

Is there any aftermarket equipment in the car?

How about trunk lamp? Have you checked the glove box lamp?

How about the "key in" / delay stuff? I don't remember how all that is wired, I'd have to look
 
  1. not looking for an argument.If you dont believe me check with a reputable electrical shop.They will tell you the same.besides there is no need to start engine anyways
 
Been doing electrical diagnostics as long as i can remember. One thing that you dont do is disconnect a battery while engine is running. Will damage other electrical components.
We dont need to make this any more difficult than it is.
 
moparfourever said:
i have done work with alternators over the years and you NEVER run an alternator with the output wire disconnected.that being said you still can test the drain from alternator by simply disconnecting the output wire and see if the battery stays up over a couple days.Do not start engine with output wire disconnected.I am betting your problem is the diodes in the alternator
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This is the way I read TJ original post. Remove output wire and check again in a couple days.

Just to be clear, could the alternator still charge (or maintain) correctly if the diodes were bad? It reads about 14.6 when the car is running. Thanks.
 
67Dart273 said:
You should not need to run the engine with the alternator disconnected. Having said that you an just pull the field wires as well

If the drain is alternator connected, simply disconnecting the output wire with engine stopped should show up as reduced battery drain.

Is there any aftermarket equipment in the car?

How about trunk lamp? Have you checked the glove box lamp?

How about the "key in" / delay stuff? I don't remember how all that is wired, I'd have to look
Click to expand...
No trunk or glove box lamp.

As far as aftermarket equipment. I did install the headlight relay and wire around kit from a member here. Both of those do attach to the output stud of the alternator.
 
Have had 4 or 5 occasions where alt performed perfectly. As alternator cooled to ambient temperature it would discharge battery. Disconnect battery and reconnect without doing anything else and fault disappears. Start vehicle and shut it off and it returns.
Reason for disconnect setup to not interrupt battery circuit after
Running engine.
My own caravan would discharge battery only when below freezing.
No fault in warm shop.
Glove box lights,radios,power antennas,trunk lamps,corroded wires under wet carpets,battery gases condensed on case missing fuse on seat belt pretensioner. I have spent endless hours chasing electrical issues. Bought some decent tools for it as well.
A non contact infra red thermometer found a few as well. Anything consuming power also produces heat.
 
demon322 said:
This is the way I read TJ original post. Remove output wire and check again in a couple days.

Just to be clear, could the alternator still charge (or maintain) correctly if the diodes were bad? It reads about 14.6 when the car is running. Thanks.
Click to expand...

Yes on the disconnect and check later without needing to run the car.

A diode is basically a one way gate for electricity.
A bad one can leave the gate open for power to run back out, so it could be normal for one to charge fine and still kill a battery if it had a bad diode.
 
TrailBeast said:
Yes on the disconnect and check later without needing to run the car.

A diode is basically a one way gate for electricity.
A bad one can leave the gate open for power to run back out, so it could be normal for one to charge fine and still kill a battery if it had a bad diode.
Click to expand...
That makes sense. I never knew that. Thank you for explaining! Will give it a shot today.
 
You really ought to pull one lead off your battery and put an ammeter in series with everything off. If it's pulling current start pulling fuses one at a time to find out where the draw is from. If that doesn't work, pull the wires off the alternator to check for a bad diode draw. It's got to be going somewhere! Your ammeter should show zero(0) amps unless you have an aftermarket radio which may pull microamps to save memory in which case you can ignore it.
 
Or you can take the alternator into a O'reily's or Auto zone and they will test it for you
 
cudajim said:
You really ought to pull one lead off your battery and put an ammeter in series with everything off. If it's pulling current start pulling fuses one at a time to find out where the draw is from. If that doesn't work, pull the wires off the alternator to check for a bad diode draw. It's got to be going somewhere! Your ammeter should show zero(0) amps unless you have an aftermarket radio which may pull microamps to save memory in which case you can ignore it.
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Yes, BUT........be careful. It is easy to screw up an ammeter because they are a SERIES device, so do this FIRST

Disconnect the battery ground, and put a large lamp bulb in series, such as a backup lamp or stop/ turn filament lamp. If it glows fairly bright, I would NOT hook up the ammeter and use the lamp instead

Make CERTAIN your multimeter is set up for the MAXIMUM current (amperage) measuring scale. If you are in doubt, post a photo of the meter, or at least the brand/ model.

With the multimeter set for maximum current, usually 10 or 20A, replace your test bulb with the meter. BE CAREFUL not to short one of the leads to something else

If you don't get a usable reading, carefully set the meter to lower scales until you get a useable reading
 
I decided to go ahead and order a replacement. I had to order the replacement alt. It came in today but is not the same as the one on my car. The new (reman) alt has only one space for field but my original one has two. There are two wires (blue and green) that hook to those spades. It is the round back alt. The cases look identical other than this. The guy at AZ asked if I had one spade or two and I said two. Anyone had a similar issue?
 
demon322 said:
I decided to go ahead and order a replacement. I had to order the replacement alt. It came in today but is not the same as the one on my car. The new (reman) alt has only one space for field but my original one has two. There are two wires (blue and green) that hook to those spades. It is the round back alt. The cases look identical other than this. The guy at AZ asked if I had one spade or two and I said two. Anyone had a similar issue?
Click to expand...

Take it back and order one for a 73 Dart or Duster.:D
You want the square back with two terminals for field.
Just so you know, most all replacement alternators come with a 2 groove pulley now.
If your current alt is a one groove you can swap them, but it doesn't matter to the way it works.
 
Weird. They look so close other than the missing field space. I’ll order the square back with two spades from the 73 tomorrow.

4A97C75A-0542-4549-BB26-90DF42374D27.jpeg
 
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