Finding An Electrical Draw - methodology question!
Thread Starter
Melting Slicks
Joined: Nov 2001
Posts: 2,214
Likes: 0
From: Casa Grande AZ
Finding An Electrical Draw - methodology question!
Hi!
Now that I'm not using my 71 as much I'm finding an electrical draw on the battery during storage. After a couple weeks it is stone dead. I put a new battery in it and I now disconnect it during storage but I'd like to fix the problem anyway.
As I understand it, if you disconnect the neg bat cable and put a meter between the post and the cable - you should see no or nearly no voltage. On mine, my meter shows 12 volts so I'm assuming that is confirmation of a draw. Correct??
Right now I have ALL the fuses out of the fusebox and I still show 12 volts at the neg cable.
Is this method correct for finding a draw??
If so, where else should I be looking besides the fused systems?
Thanks!
Now that I'm not using my 71 as much I'm finding an electrical draw on the battery during storage. After a couple weeks it is stone dead. I put a new battery in it and I now disconnect it during storage but I'd like to fix the problem anyway.
As I understand it, if you disconnect the neg bat cable and put a meter between the post and the cable - you should see no or nearly no voltage. On mine, my meter shows 12 volts so I'm assuming that is confirmation of a draw. Correct??
Right now I have ALL the fuses out of the fusebox and I still show 12 volts at the neg cable.
Is this method correct for finding a draw??
If so, where else should I be looking besides the fused systems?
Thanks!
Tech Contributor
Joined: Aug 1999
Posts: 15,135
Likes: 3,939
From: Connecticut, USA
Re: Finding An Electrical Draw - methodology question! (lbell101)
Hi Larry,
I think you got the method down, now you have to find the problem. I don't have a schematic in front of me but a couple of things to check.
1- Is the wiper door up? I had a drain on the system when the micro switch was made by the wiper door.
2- Any aftermarket alarm or radio? Found draws from both on different cars.
Keep us posted on what you find.
Gary
I think you got the method down, now you have to find the problem. I don't have a schematic in front of me but a couple of things to check.
1- Is the wiper door up? I had a drain on the system when the micro switch was made by the wiper door.
2- Any aftermarket alarm or radio? Found draws from both on different cars.
Keep us posted on what you find.
Gary
Melting Slicks
Joined: Aug 1999
Posts: 3,123
Likes: 13
From: Hollywood, Florida
Re: Finding An Electrical Draw - methodology question! (lbell101)
Larry,
I might be wrong but.....shouldn't you be measuring amps being drawn thru NOT voltage???
My basic electronics knowledge is fuzzy :yesnod:
I might be wrong but.....shouldn't you be measuring amps being drawn thru NOT voltage???
My basic electronics knowledge is fuzzy :yesnod:
Instructor
Joined: Jun 2001
Posts: 229
Likes: 1
From: Uxbridge MA
Re: Finding An Electrical Draw - methodology question! (lbell101)
Use the meter to measue amps (Highest setting possible). Place black lead on neg battery post, place red lead on disconnected neg cable. I found my vehicle was drawing .3A when off and all doors closed. I traced it back to a bad alternator with a bad diode that was leaking back to ground. After replacing the alternator my draw was ~.01A Good luck....
--Andy
--Andy
Burning Brakes
Joined: Sep 2000
Posts: 922
Likes: 0
From: Maine
Re: Finding An Electrical Draw - methodology question! (shoptek)
Yeah, you need to put your meter between one of the battery cables and the battery post it came from, make sure you select the highest "amp" range possible and see if you can read something.
Racer
Joined: Apr 2000
Posts: 499
Likes: 0
From: Kristiansand
Re: Finding An Electrical Draw - methodology question! (lbell101)
I would say that method is not usable.
Due to the very high input resistance of your meter even the smallest load on the battery (f.ex. clock) will make it show 12V. And it will tell you nothing about the magnitude of the leak.
You need to use the same hookup, but set the meter to measure current (Amp).
Be careful though if your meter doesn't have a built in fuse. Most cheap meters are unfused on the high current (10A) setting.
If you have a large leak or you make a short you might fry the meter.
Due to the very high input resistance of your meter even the smallest load on the battery (f.ex. clock) will make it show 12V. And it will tell you nothing about the magnitude of the leak.
You need to use the same hookup, but set the meter to measure current (Amp).
Be careful though if your meter doesn't have a built in fuse. Most cheap meters are unfused on the high current (10A) setting.
If you have a large leak or you make a short you might fry the meter.
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Thread Starter
Melting Slicks
Joined: Nov 2001
Posts: 2,214
Likes: 0
From: Casa Grande AZ
Re: Finding An Electrical Draw - methodology question! (Smokehouse69)
Thanks guys!
Amps - damn, I should have figured that one out.
None of my testers have full amp capability (mA only) so I rigged up a test light from a taillight bulb and some wires. The only time it will light is when the courtesy fuse is put in. So it's that circuit I believe.
Also, it was getting dark while I was doing this so I was able to notice that the interior lights sometimes come back on. This is after the door is closed for 10 minutes or so. So I'm pretty sure that must be the problem!
Thanks for the help!!!
Amps - damn, I should have figured that one out.
None of my testers have full amp capability (mA only) so I rigged up a test light from a taillight bulb and some wires. The only time it will light is when the courtesy fuse is put in. So it's that circuit I believe.
Also, it was getting dark while I was doing this so I was able to notice that the interior lights sometimes come back on. This is after the door is closed for 10 minutes or so. So I'm pretty sure that must be the problem!
Thanks for the help!!!
Safety Car
Joined: Jan 2001
Posts: 4,660
Likes: 3
From: South Central Louisiana
St. Jude Contributor
Re: Finding An Electrical Draw - methodology question! (lbell101)
Larry, I had this problem years ago with a Nissan pickup. A battery killing draw in the courtesy circuit. The culprit was the delay box for the courtesy light. A friend of mine had the same problem, it was a light bulb thats filament was touching ground in the bulb, but not lighting. In your case I would also check for a door switch making contact at times when the door is closed.
And I would go ahead and keep useing your method to check for draw. Although a DC amp meter would be best, sometimes they are hard to come by and not necessary in this case. Just eliminate your known draws (clock, radio memory) so you dont get thrown off.
[Modified by 71,454,4spd, 9:16 PM 9/8/2002]
And I would go ahead and keep useing your method to check for draw. Although a DC amp meter would be best, sometimes they are hard to come by and not necessary in this case. Just eliminate your known draws (clock, radio memory) so you dont get thrown off.
[Modified by 71,454,4spd, 9:16 PM 9/8/2002]
