Drain in one hour
5th Gear
Joined: Mar 2010
Posts: 5
Likes: 0
From: Fraser Michigan
I was always under the impression that when using a light to check circuits that the brighter the light the more current draw. If the current is more than the light can support it will burn out due to too much current. As stated early in the post the amp meter fuse was probably blown due to the excess current or the meter was not set up to read amps. If what we were told is correct and he was getting 12 VDC from the negative post to the negative cable while it was disconnected from the battery and the positive cable was disconnected from the starter lug it seems to me that the positive cable was grounding out somewhere. I hope he tells us what was wrong in a follow up post.
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
You measure voltage in parallel and current ( amps ) in series, you can't disconnect the cable and read voltage from the battery terminal to the disconnected cable. You can measure current in this manner. 
There seems to be a bit of confusion on how to measure voltage and current, I had this old s/w on my computer from my high tech days
but if it can save a meter or a test light I thought I'd post it. It shows you need to break the line and insert an ammeter in series to test for current and you just put a voltmeter across the load or source when checking voltage Some know this but this is for those who might not be aware
And don't start the motor with the ammeter in the circuit it will blow, this is to check for current leakage with the ignition off. Also a test light would go where the voltmeter is, if you put it where the ammeter is it will blow. The test that should be performed to find any leakage current is the one with the ammeter in the positive circuit. Depending on what is powered when the ignition is off, (not much on our C3's) the current measured should be very low in milliamp range if anything at all. Hope this helps
There seems to be a bit of confusion on how to measure voltage and current, I had this old s/w on my computer from my high tech days
but if it can save a meter or a test light I thought I'd post it. It shows you need to break the line and insert an ammeter in series to test for current and you just put a voltmeter across the load or source when checking voltage Some know this but this is for those who might not be aware And don't start the motor with the ammeter in the circuit it will blow, this is to check for current leakage with the ignition off. Also a test light would go where the voltmeter is, if you put it where the ammeter is it will blow. The test that should be performed to find any leakage current is the one with the ammeter in the positive circuit. Depending on what is powered when the ignition is off, (not much on our C3's) the current measured should be very low in milliamp range if anything at all. Hope this helps
Last edited by MotorHead; Mar 30, 2010 at 05:31 PM.
5th Gear
Joined: Mar 2010
Posts: 5
Likes: 0
From: Fraser Michigan
Good sketch and it shows what we have been saying that there is nothing therer but the positive cable to the starter! I use both methods, it depends on what you are looking for or testing. It is the simple things that will bite you like lights left on, brake lite switch sticking. I found a loose screw in a cigarette lighter socket and it would blow fuses intermittently, or when you made a hard turn and the screw would move. His method of testing would work, but if he had the headlights on, it would lok like a short or heavy current draw. Think maybe he is pulling our chain?
7th Gear
Joined: Mar 2010
Posts: 7
Likes: 0
I have the same problem with my car. I pulled the wiper fuse and the drain was still there. Disconnected the wiper motor plug and the battery drain is gone. Now I have to find out why the motor is draining the battery. Just another day in a life with my car.
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7th Gear
Joined: Mar 2010
Posts: 7
Likes: 0
Well, I thought I pulled the wiper fuse. I pulled the left side of the fuse panel and took it for granted that the wiper fuse was on that side. Sorry, about the misleading information.
I had the Battery connected for a while and went to feel the wiper motor and it was warm, my wipers do not work either. So I disconnected the motor and the drain went away. I hope yours is the same.
I had the Battery connected for a while and went to feel the wiper motor and it was warm, my wipers do not work either. So I disconnected the motor and the drain went away. I hope yours is the same.
7th Gear
Joined: Mar 2010
Posts: 7
Likes: 0
Well, went out to the car and pulled the wiper fuse, because I felt bad about the info I gave you before and the drain is still there. So I think it is the wiper motor with your car also. It is a three prong plug that disconnects the wiper motor. I connected my Battery for while and then went to feel the motor, it was warm and like I said , my wipers do not work either. It's worth a look.
7th Gear
Joined: Mar 2010
Posts: 7
Likes: 0
My Battery drain turn out to be the wiper motor did not cycle completely, to the parked position. If the wiper door would work, I may have found the problem sooner. Had to manually open the wiper door and turn the wipers on and off to fix the problem. Could have been worse!
Team Owner
Joined: Jul 2004
Posts: 40,412
Likes: 792
From: Redondo Beach, California
I've long since forgotten the details, however the wiper motor would spontaniously turn itself "on" when the car was parked. The wiper blades would rise up and hit the closed wiper door. Of course with no vacuum, there was no way the wiper would actually start working. With the blades suck against the inside of the door, the wiper motor was in a stalled conditioned and would drain the battery. I've since had my 68 wiper restored and installed new harnesses and vacuum controls. No problem.