similarity between 77 and 78
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Pro
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From: Milford, CT
similarity between 77 and 78
I need to do some electrical troubleshooting on my 77. It has a mystery battery drain. I found an Electrical troubleshooting guide online for the 1978 model and was wondering if the electrical systems between the 77 and the 78 are close enough to use it.
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Pro
Joined: May 2015
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From: Milford, CT
Here is the problem. I have a Fluke multimeter. I also have a 12v test light. My battery is in good shape (actually I have 2 of them).
I installed a fresh battery and the voltage read 12.48v. I checked it periodically all morning and it had dropped to 12.37v. The car started perfectly everytime and when it is running the voltage shows 13.6v to 14.1v. I have a brand new alternator on the car. Anyway... I figured it must have been the old aftermarket radio/antenna booster that was in the car that was causing the original drain (the battery would drain down to not even able to light the dome light after less than 2 hours). I removed the radio and all the wiring for the aftermarket stuff and it appeared that I solved the problem. I went back to the car around 4:00pm and checked the battery with a meter and it was down to around 11 volts and wouldn't even light up the dome light. I couldn't find any draw using the meter or the test light so there was no sense in pulling fuses.
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Pro
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From: Milford, CT
I tried that first. I also got the battery load tested. I have 2 of them. One is a few years old, the other is a few weeks old. Both tested fine. When I fully charged the brand new one it read around 12.8v. After 3 days of just sitting on my garage floor it was at 12.68v so its not discharging by itself.
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From: McHenry Illinois
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From: Milford, CT
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From: Machesney Park IL
For a quickie, disconnect the negative cable at the battery and connect the test light between the cable and battery post. With everything off(don't forget the interior light timer delay), the test light should be barely lit, if at all. If it is bright, start removing fuses to try and narrow down the circuit that is being naughty to you.
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Pro
Joined: May 2015
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From: Milford, CT
For a quickie, disconnect the negative cable at the battery and connect the test light between the cable and battery post. With everything off(don't forget the interior light timer delay), the test light should be barely lit, if at all. If it is bright, start removing fuses to try and narrow down the circuit that is being naughty to you.
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From: Charlotte NC
Then you do not have a power drain....PERIOD. NO light on your test light means NO power going to 'something' that is taking amps out of the battery.
I do not use the test light method myself....even though I have in the past. I got the tool that allows me to see the actual value of amp draw...because repairing all year models of Corvettes...I had to see what the amp draw actually was. Because I have come across many newer Corvettes that start off fine on the amp draw but I can watch my tool and the amp draw increases to the point where it will drain the battery overnight if left connected. And...if I use the test light method on a 1986....the test light will be so bright that you would swear that there is a serious drain...when actually ...there is a drain.... but it is NOT at the point of worrying about the battery going dead overnight or even in a month of sitting. Because the 1984-1996 Corvettes have a drain in the system.
DUB
I do not use the test light method myself....even though I have in the past. I got the tool that allows me to see the actual value of amp draw...because repairing all year models of Corvettes...I had to see what the amp draw actually was. Because I have come across many newer Corvettes that start off fine on the amp draw but I can watch my tool and the amp draw increases to the point where it will drain the battery overnight if left connected. And...if I use the test light method on a 1986....the test light will be so bright that you would swear that there is a serious drain...when actually ...there is a drain.... but it is NOT at the point of worrying about the battery going dead overnight or even in a month of sitting. Because the 1984-1996 Corvettes have a drain in the system.
DUB
Thread Starter
Pro
Joined: May 2015
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From: Milford, CT
Then you do not have a power drain....PERIOD. NO light on your test light means NO power going to 'something' that is taking amps out of the battery.
I do not use the test light method myself....even though I have in the past. I got the tool that allows me to see the actual value of amp draw...because repairing all year models of Corvettes...I had to see what the amp draw actually was. Because I have come across many newer Corvettes that start off fine on the amp draw but I can watch my tool and the amp draw increases to the point where it will drain the battery overnight if left connected. And...if I use the test light method on a 1986....the test light will be so bright that you would swear that there is a serious drain...when actually ...there is a drain.... but it is NOT at the point of worrying about the battery going dead overnight or even in a month of sitting. Because the 1984-1996 Corvettes have a drain in the system.
DUB
I do not use the test light method myself....even though I have in the past. I got the tool that allows me to see the actual value of amp draw...because repairing all year models of Corvettes...I had to see what the amp draw actually was. Because I have come across many newer Corvettes that start off fine on the amp draw but I can watch my tool and the amp draw increases to the point where it will drain the battery overnight if left connected. And...if I use the test light method on a 1986....the test light will be so bright that you would swear that there is a serious drain...when actually ...there is a drain.... but it is NOT at the point of worrying about the battery going dead overnight or even in a month of sitting. Because the 1984-1996 Corvettes have a drain in the system.
DUB
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From: Charlotte NC
AND....something is 'fishy'...because the wiper is NOT a circuit that should be alive with current with the ignition key OFF....depending on which connector you removed.
What was you ammeter reading before you found the 'drain'????
DUB
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From: Milford, CT
GREAT...BUT by your last post...no light on your test light is saying you have no power drain...unless it was not connected correctly....meaning not making good contact.
AND....something is 'fishy'...because the wiper is NOT a circuit that should be alive with current with the ignition key OFF....depending on which connector you removed.
What was you ammeter reading before you found the 'drain'????
DUB
AND....something is 'fishy'...because the wiper is NOT a circuit that should be alive with current with the ignition key OFF....depending on which connector you removed.
What was you ammeter reading before you found the 'drain'????
DUB
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Joined: Feb 1999
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From: Tampa Bay FL
Here is the problem. I have a Fluke multimeter. I also have a 12v test light. My battery is in good shape (actually I have 2 of them).
I installed a fresh battery and the voltage read 12.48v. I checked it periodically all morning and it had dropped to 12.37v. The car started perfectly everytime and when it is running the voltage shows 13.6v to 14.1v. I have a brand new alternator on the car. Anyway... I figured it must have been the old aftermarket radio/antenna booster that was in the car that was causing the original drain (the battery would drain down to not even able to light the dome light after less than 2 hours). I removed the radio and all the wiring for the aftermarket stuff and it appeared that I solved the problem. I went back to the car around 4:00pm and checked the battery with a meter and it was down to around 11 volts and wouldn't even light up the dome light. I couldn't find any draw using the meter or the test light so there was no sense in pulling fuses.
I installed a fresh battery and the voltage read 12.48v. I checked it periodically all morning and it had dropped to 12.37v. The car started perfectly everytime and when it is running the voltage shows 13.6v to 14.1v. I have a brand new alternator on the car. Anyway... I figured it must have been the old aftermarket radio/antenna booster that was in the car that was causing the original drain (the battery would drain down to not even able to light the dome light after less than 2 hours). I removed the radio and all the wiring for the aftermarket stuff and it appeared that I solved the problem. I went back to the car around 4:00pm and checked the battery with a meter and it was down to around 11 volts and wouldn't even light up the dome light. I couldn't find any draw using the meter or the test light so there was no sense in pulling fuses.
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Joined: Apr 2009
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From: Charlotte NC
This just does not make any sense due to the wiper motor is a switched part. Meaning that you have to have the key ON in order for it to work...but yet...your interior lights are not switched power. They are hot at all times...like your headlights.
Someone has gotten in this car and messed around.
DUB
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Joined: May 2015
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From: Milford, CT
Thanks for the information.
This just does not make any sense due to the wiper motor is a switched part. Meaning that you have to have the key ON in order for it to work...but yet...your interior lights are not switched power. They are hot at all times...like your headlights.
Someone has gotten in this car and messed around.
DUB
This just does not make any sense due to the wiper motor is a switched part. Meaning that you have to have the key ON in order for it to work...but yet...your interior lights are not switched power. They are hot at all times...like your headlights.
Someone has gotten in this car and messed around.
DUB
It doesn't make sense to me either but I read another thread on this forum with somebody with the exact same problem. There was no resolution on that thread. The only thing I can think of is because there are multiple wires (not just hot and ground) going to the wiper motor maybe one of them is constant unswitched power and that's the wire that is bad.