Key off battery drain

[ralt962 11]

It appears I have an issue with key off battery drain.  I have not yet dug into this, but was wondering if there is a common issue out there that you have seen.  I have a complete rebuild with new circuit board.  I had gone through the harnesses completely prior to assembly.  One issue from a different thread is the grounding of the gauge posts.  I will be pulling the dash pad for the gauge issue.

My original clock works and has been running but I cant believe that would drain a new battery.  

Great forum.  You have been tremendous help through my restoration.

[gordonr 4]

Its best just to see if you have excessive draw. Its very easy to check. 1st You need a hand held volt meter with a 10 amp function. Disconnect the negative cable. With your meter setup  in "amps" hook up one lead to the  post on on your battery the other lead on the cable.  Any  circuit drawing current in your car has to pass thru the meter and there is no guessing.  As a daily driver .050 mA or less is acceptable. For cars that can sit for a month or two it is not. I like to see .020 mA or less. 

[Midlife 814]

Here's my stock advice for finding excessive current draw that I provide every customer of mine:

First, always install electrical wiring with the battery disconnected.

Physically install the underdash harness with fuses.  Connect all underhood and taillight harnesses.

 

When ready to check out the harness, close all doors, turn off all lights, accessories, etc.  Make sure both battery connectors are disconnected.  Connect the positive battery cable to the starter solenoid.  Leave the negative terminal disconnected from the battery.  Then use a digital volt meter to measure the current draw across the battery.  Place one probe of the DVM on the negative battery cable terminal, and the other probe on the negative battery post.  Be sure that the DVM is set to amps, DC.  If there are no shorts in the wiring connections, the reading should be on the order of 30 milliamps or less.  Anything above 1 amp indicates some accessory is on; readings above 10 amps (may blow the fuse on the DVM) indicates a dead short.

 

If you have a short, disconnect all other wiring from the starter solenoid post where the battery connects and re-measure the current.  If current drops, the source is the underdash wiring harness or the harness from the starter solenoid to the firewall.  Reconnect the wiring to the starter post and then disconnect the underhood harness from the firewall and test again to isolate the source of the short. 

If the short is not in the underhood or underdash harness, the problem lies in the alternator or voltage regulator.  Disconnect each of these in turn to isolate the source.

 

If the short or high current comes from the underdash region, keep the battery negative side disconnected and remove one fuse at a time.  Measure the current as above.  If you now see low current, there is either a short or an item on that particular fuse circuit is on.  Turn off that item and continue checking.

 

Eventually, you’ll have low current readings with all fuses installed and all wiring connected.  At that time, and only at that time, is it safe to connect the negative battery cable to the battery.

 

Eventually, you’ll have low current readings with all fuses installed and all wiring connected.  This series of tests checks all of the battery directly powered systems.  To check the Accessory systems, now repeat all of the tests above with the ignition key in the ACC position.  The current with the key in the ACC position may be up to 1 amp or so.  When all of the tests are done and no anomalous current is noted, at that time, and only at that time, is it safe to connect the negative battery cable to the battery.

[Brian Conway 264]

Great descriptions and directions.  Brian 

[1969_Mach1 333]

For odd battery drains, after checking the obvious items like something turned on.  The first go to place is the alternator.  If two or more diodes short in the rectifier bridged, the alternator will drain the battery with the key off.  The alternator will still operate but the maximum amperage output will be a little low.  So if there is a drain using gordonr's method with a multimeter, disconnect the alternator and see if that has any affect.

If you don't have a multimeter, on older cars like these you can use a test light.  Disconnect the positive battery cable, clip the lead to the positive battery post and touch the positive battery cable end with the other end.  If the light glows, even dim, there is too much current flow and will drain the battery.

[Midlife 814]

5 hours ago, 1969_Mach1 said:

For odd battery drains, after checking the obvious items like something turned on.  The first go to place is the alternator.  If two or more diodes short in the rectifier bridged, the alternator will drain the battery with the key off.  The alternator will still operate but the maximum amperage output will be a little low.  So if there is a drain using gordonr's method with a multimeter, disconnect the alternator and see if that has any affect.

If you don't have a multimeter, on older cars like these you can use a test light.  Disconnect the positive battery cable, clip the lead to the positive battery post and touch the positive battery cable end with the other end.  If the light glows, even dim, there is too much current flow and will drain the battery.

It is far safer to do this with the negative side of the battery vice positive side.  You can inadvertently short the battery with your wrench when connecting the positive side with the negative side already connected; you cannot short connecting the negative side last.

[gordonr 4]

6 hours ago, 1969_Mach1 said:

For odd battery drains, after checking the obvious items like something turned on.  The first go to place is the alternator.  If two or more diodes short in the rectifier bridged, the alternator will drain the battery with the key off.  The alternator will still operate but the maximum amperage output will be a little low.  So if there is a drain using gordonr's method with a multimeter, disconnect the alternator and see if that has any affect.

If you don't have a multimeter, on older cars like these you can use a test light.  Disconnect the positive battery cable, clip the lead to the positive battery post and touch the positive battery cable end with the other end.  If the light glows, even dim, there is too much current flow and will drain the battery.

      Lol, Back in the early 80's I remember using a 20 foot harness, 2 alligator clips and 194 socket and bulb walking around the cars looking for drains based on the illumination. Then when electronics (BCM's) came on the seen I moved up to a 3 watt 1 ohm resistor and read mV  across the resistor for a drain reading  as most hand held meters amp functions were lacking.  Also the standard was pulling fuses for locating the offending circuit . Today s cars you cant do that unless you want spend all day on it. The standard now is reading for a voltage drop across  fuses with  your meter set to millivolts as pulling a fuse can wake up computers and ruin your test. It also takes two meters for a tech perform a test. I miss the good  ole days!

[ClubSport 29]

Hi , I had the same issue on my stock alternator , it appeared to be one the diodes to be fried and draining the battery. Bought and installed a power master internally regulated and it never appeared again.

[1969_Mach1 333]

6 hours ago, gordonr said:

      Lol, Back in the early 80's I remember using a 20 foot harness, 2 alligator clips and 194 socket and bulb walking around the cars looking for drains based on the illumination.

Well, now you have an idea of my age.  Using a test light as well as DVOM's was a method taught by General Motors back when I was a mechanic.  Yes, we use to say mechanic and not technician and it didn't offend anybody.  No doubt I'm not knowledgeable as you are with todays automotive electronics which is fine. 

[ralt962 11]

Outstanding advice.  New battery and I did install the harnesses with the battery disconnected, not in the car.  

I have a pretty good DVOM so I'll start there.  It drained a new battery pretty quickly, so I'll do the alternator after checking the overall drain test.  The target numbers will be very helpful.  

I still have to go back in and recheck the gauge nuts, likely shorted there since i'm not getting much gauge movement.  

[ralt962 11]

You guys nailed it.  Used your method across the ground.  Alternator disconnected dropped it to zero on my DVOM.  I'm a little surprised I didnt have some drain like Gordonr mentions.  It might not be able to read that low.  But great find I would have spent a long time going through the dash harness before looking at the alternator.  

Thank  you.  Everyone has been extremely helpful on this site.

[1969_Mach1 333]

Glad to hear you found the culprit.  It's always best to check the simple stuff first.  Somewhat common for alternators to cause a battery drain.  Well, at least in my day when I worked as a mechanic.

[gordonr 4]

Glad to see you figured it out with no guessing. With electrics you shouldn't be surprised, outcomes for the same symptom can and will have  different  causes.  Being consistent with procedures for locating drains will always have a good outcome. If you saw no other drains then I assume you have no electronics in your car that require memory power. For example a viper remote start will draw around 43mA or a standard cd player will be 5 to 10mA as a couple examples. Also another tip, if your meter shows nothing doing the test open a door (turns on interior lights)or turn on the park lights to insure your meter doent have a blown internal fuse and connections are good as operating as those items will actually work.