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I replaced the battery on 68 last night. For some reason, when I hit the brakes or use the turn signal the amp meter shows a big drain.
The last battery went completely out. Any suggestions on how to track down the short?
Why do you think it is a short as opposed to the alternator?
Have you used a voltmeter to check alternator output?
Have you checked the alternator plug with the two wires for corrosion or a broken wire?
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
Check the output at the alternator and your voltage regulator. Stock 68 alternators were somewhere around 60 amps....not much especially if you upgraded the lights and stereo. The regulator could be bad and not putting out enough volts to charge the battery.....remember on the 68 the wiper override will drain your battery as well if it’s not in the fully off position ( connected to ground)
Check the output at the alternator and your voltage regulator. Stock 68 alternators were somewhere around 60 amps....not much especially if you upgraded the lights and stereo. The regulator could be bad and not putting out enough volts to charge the battery.....remember on the 68 the wiper override will drain your battery as well if it’s not in the fully off position ( connected to ground)
I put an amp meter on the alternator posts and getting12.3 with the engine off and when idle and the turn signal on it goes from 12.3 to 11.5 .
Sounds like I should be getting more like 60???
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
To read amps the electricity has to travel through the meter only. So you would have to have you're meter set for high amps, disconnect the wire from the alternator to the voltage regulator and read between the post and wire you disconnected. It should put out the amps required you can check it through a few smooth rpm changes above idle. Then reconnect it and see what's coming out of the regulator the same way. You can have an auto parts store read the alternator for free usually. I would call and see if the are equipped to test voltage meters. The alternator should be putting out 14 volts with the motor running above idle
For an over night drain I disconnect the positive lead at the battery and connect to the battery post and the positive lead and then see if there is a draw with the motor off. If there is I just start pulling fuses and see if it stops.
I disconnected the positive lead off the battery and checked for amps between the battery post and the positive cable with the engine off and was reading 12.3. I will start pulling fuses.
Thanks
I disconnected the positive lead off the battery and checked for amps between the battery post and the positive cable with the engine off and was reading 12.3. I will start pulling fuses.
Thanks
Just to be clear, you are sure the meter is set for AMPS, not VOLTS?
I put an amp meter on the alternator posts and getting12.3 with the engine off and when idle and the turn signal on it goes from 12.3 to 11.5 .
Sounds like I should be getting more like 60???
Sorry just got access
yes using the amps side
but good question
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
Should only be getting 60 amps when the motor is running, it would be the output of the alternator. I dont know how many amps the lamps would be using. I know the fuse is 20 amps but is should go from close to zero to the amps needed to light the light.
Turn off everything and take a reading between the post and the power lead, it should be close to zero. IF it isnt then note how many amps are being used and start removing fuses and make notes of the amps drop each time. It should not move until you find the problem and it should drop to near zero. If you start the car you would be able to see how many amps are coming from the alternator but do that at the alternaotr output. You have to very careful doing it that way and I suggest taking it to any auto parts store to test the output if it comes to that. Usually the best way to test the alternator is at the parts store on a big machine.
Last edited by Rescue Rogers; Aug 20, 2020 at 08:18 PM.
I do not want to discourage your from playing with your car but you might want to get some assistance. Some of the values that you are reporting are not making sense??? Why don't you take a picture of what it is that you are reading, your meter, and where the connections are hooked up when you take these readings.
As mentioned earlier - you may just want to remove your alternator and take it in to your local parts store and get it tested. My local parts stores check them for free. It would be a good place to start.
Last edited by carriljc; Aug 20, 2020 at 08:25 PM.
Here are three pictures:
1st reading across posts with key off
2nd reading across posts with the engine at idle
3rd reading between the positive post and cable with the key off reading engine at idle Reading between post and cable with key off reading key off
Last edited by Cobfree; Aug 21, 2020 at 12:31 PM.
Reason: typed wrong
From: Loud, Raw and Dangerous 1968 327 4S in Southern California
Picture 2 is still reading Volts...would need to put the red lead in the other position on the meter marked 200ma/DCA. Also with such a low rating it is possible you can blow the fuse if the current is over 200 ma which if ignition is on will likely happen. If you are looking for a very low current draw this meter might work but with the ignition kept off.
Last edited by Redvette2; Aug 21, 2020 at 12:48 PM.
And you want to ensure that the doors are closed (no lamps on inside)..... or anything else on. Even then, if you have a large fault you may blow the fuse anyway so be ready with a replacement or your troubleshooting will get discombobulated while you get another fuse.
As best as I can tell (pic is fuzzy) adjust your multimeter connection and selector as follows:
Move the red lead to position "1" in the below drawing.
Select 200 as indicated for position "2" in the below drawing.
Originally Posted by Redvette2
Picture 2 is still reading Volts...would need to put the red lead in the other position on the meter marked 200ma/DCA. Also with such a low rating it is possible you can blow the fuse if the current is over 200 ma which if ignition is on will likely happen. If you are looking for a very low current draw this meter might work but with the ignition kept off.
Last edited by carriljc; Aug 21, 2020 at 02:48 PM.
By the way. It would appear that your alternator is not doing well at idle. I would expect between 13.5vdc and 14 vdc when idling.
Even the "good" alternator on my 1968 (61 or 63 amp? I don't remember) was iffy, at best, when idling, at night, with all the lights on, and the vent fan running......
Looks like the alternator might be bad. Its only a couple of years old. When I changed the leads to 200m DCA with the engine at idle, the reading was 00.0.
Is it normal for power to be consumed as in the fist photo with everything off?
Looks like the alternator might be bad. Its only a couple of years old. When I changed the leads to 200m DCA with the engine at idle, the reading was 00.0.
Is it normal for power to be consumed as in the fist photo with everything off?
You're assessment that the alternator is bad is the most likely conclusion based on your posts/pics.
In the first photo you're meter is seeing battery voltage as "something" is completing a circuit (courtesy lights, bad alternator, clock, etc).
Your voltage drops when you start the car, and drops further when you turn on the lights, signals, etc (and you see the same discharge state on your amp meter) because your alternator is not putting out any current to support the demand so everything is running off the battery.
So, most likely, your alternator is bad OR perhaps the voltage regulator.
Battery Drain
