Electrical problem
Thread Starter
Instructor
Joined: Jul 2013
Posts: 206
Likes: 103
From: Macedonia Ohio
Electrical problem
1968 coupe showing a high resistance short to ground with the car off. The battery drains overnight to the point that car won't start. Pulling the instrument fuse results in no short. With the fuse pulled all gages work accept the water temperature. Gage. With the fuse in the the water temp gage works as it should. As I understand it, the 12 volts to the gage is switched through the ignition switch. Could the ignition switch be the culprit.
Burning Brakes
Joined: Dec 2017
Posts: 1,043
Likes: 414
2023 C3 of the Year Finalist - Modified
High resistance short?
A short implies a low resistance.
If you are having a battery drain and there is no evidence of a short, then I would investigate all non-linear circuit elements in the car, anything that is a semi conductor.
the voltage regulator on the alternator is a common culprit.
try disconnecting your alt and see if the drain goes away.
A short implies a low resistance.
If you are having a battery drain and there is no evidence of a short, then I would investigate all non-linear circuit elements in the car, anything that is a semi conductor.
the voltage regulator on the alternator is a common culprit.
try disconnecting your alt and see if the drain goes away.
Burning Brakes
Joined: Sep 2016
Posts: 912
Likes: 402
From: Dutchess county New York
If you can measure the fault reliably with a meter then pull fuses one at a time and see if the fault goes away, at least hat would help you narrow it down.
A battery disconnect on these old cars is usually a good idea even without a parasitic drain.
A battery disconnect on these old cars is usually a good idea even without a parasitic drain.
Race Director
Joined: Mar 2017
Posts: 11,710
Likes: 4,363
From: Virginia
It's either fused (pull all the fuses), or not.
If not fused, it's either a pinched wire between the battery and fuse panel, or more likely your alternator.
I'd start with the alternator myself.
If not fused, it's either a pinched wire between the battery and fuse panel, or more likely your alternator.
I'd start with the alternator myself.
Safety Car
Joined: May 2001
Posts: 4,711
Likes: 1,624
From: Fairfax Virginia
Harbor Freight carries these devices that plug into a fuse slot and then it shows how much current is flowing through the circuit. They were less than $25 when i bought mine.
On the 1968 C3 the most common grounding issues was mentioned by Richard454 and that is to check the position of the windshield wiper bypass switch which allows you to stop the wipers to change them. If that switch is left on it will drain your battery down. Be sure to check the entire wiper system for any problems.
Other places to look are at you alternator and be sure that it is not the culprit, bad diodes in the diode bridge can suck power continuously. This too is way to common a failure mode even in this day and age.
I had an interior light switch that was shorting and pulling a tiny current which was a slow drain on the battery.
On the 1968 C3 the most common grounding issues was mentioned by Richard454 and that is to check the position of the windshield wiper bypass switch which allows you to stop the wipers to change them. If that switch is left on it will drain your battery down. Be sure to check the entire wiper system for any problems.
Other places to look are at you alternator and be sure that it is not the culprit, bad diodes in the diode bridge can suck power continuously. This too is way to common a failure mode even in this day and age.
I had an interior light switch that was shorting and pulling a tiny current which was a slow drain on the battery.
Le Mans Master
Joined: Jan 2001
Posts: 6,631
Likes: 1,340
bg725
You may also have interrupted the 1968 wiper system operation and relay behind the tach is staying energized (and there is nothing wrong with the system other than the goofy design).
A quick check is to listen for the relay as you disconnect and connect the negative battery terminal. It is rather obvious when it CLICKS.
Let me find a post on that.....in case it is just and interrupted wiper start......
You may also have interrupted the 1968 wiper system operation and relay behind the tach is staying energized (and there is nothing wrong with the system other than the goofy design).
A quick check is to listen for the relay as you disconnect and connect the negative battery terminal. It is rather obvious when it CLICKS.
Let me find a post on that.....in case it is just and interrupted wiper start......
Le Mans Master
Joined: Jan 2001
Posts: 6,631
Likes: 1,340
bg725
FYI - in case it is a case of wiper start interruption:
https://www.corvetteforum.com/forums...post1607052246
FYI - in case it is a case of wiper start interruption:
https://www.corvetteforum.com/forums...post1607052246
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Race Director
Joined: Mar 2016
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From: Napa Valley California
Have you done any recent maintenance to the car?
Check any new electical components you installed to make sure the new parts aren’t causing your drain.
Check any connections to electrical component to make sure everything is taught.
Another thing to consider is, the wiring insulation on our cars is 50+ years old, it becomes brittle with age and sometimes the slightest movement can crack the insulation and cause intermittent shorts.
After checking the items listed by the other’s, start following all the wires running adjacent to the frame, engine and anything metal to see if any wire insulation has rubbed and exposed the wire strands.
The best advice, listen to the forum members above, they know the electrial systems on our cars and Richard454 is considered the electrical guru.
Check any new electical components you installed to make sure the new parts aren’t causing your drain.
Check any connections to electrical component to make sure everything is taught.
Another thing to consider is, the wiring insulation on our cars is 50+ years old, it becomes brittle with age and sometimes the slightest movement can crack the insulation and cause intermittent shorts.
After checking the items listed by the other’s, start following all the wires running adjacent to the frame, engine and anything metal to see if any wire insulation has rubbed and exposed the wire strands.
The best advice, listen to the forum members above, they know the electrial systems on our cars and Richard454 is considered the electrical guru.