Hello guys. So I’m helping my girlfriend’s dad get his 68’ C3 back on the road. It runs fine but he doesn’t like to take it out because he has had a problem for quite some time where the battery will drain within a few days if left connected. It had stranded him a few times at the grocery store where he will come out and the battery will be dead. With a fairly new battery at that. Sounds like some kind of parasitic draw to me. So I got to power probing around in the engine bay and realized that simply by connecting the battery (no key in the ignition, just simply connecting the battery) that the alternator, starter relay, wiper motor and various other things in the engine bay all have 12 volts. Originally I discovered this and thought that it could be the ignition switch, so we swapped out for a new one only for the problem to still exist with the new one installed. Upon removing the old ignition switch I did notice that there is no ground wire that connects to the ignition switch. I thought that was odd. So 3 questions here:

1. Is it normal that by simply connecting the battery, with no key in the ignition, that pretty much everything in the engine bay should have 12 volts? If not where could this power to everything in the engine bay, minus the coil, be coming from? Could wires be contacting each other somewhere?

2. Is it normal that the ignition switch does not have a ground running into it? There is a tab on the ignition switch where a wire can connect on the pigtail but there’s just no wire that runs into it.

3. As I mentioned when you simply hook the battery up everything has 12.2 volts. When you turn the key into the accessory/run position, it drops down to 11.1. Is this normal?

Thank you everyone.

 

I’m no electrical guru so I can’t answer your 3 questions.
Although what you described doesn’t sound normal.

On the 68 Corvette forum on FB, they were discussing that 68’s had a metal part in the center rear storage compartment that kept the door from activating the light in the compartment when the door was shut. If that metal part was missing, the battery would drain.
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You might want to start by cleaning your battery connections and all grounds, battery to frame, frame to engine. The results may surprise you.

 

Jason92
Here. Follow this link for common 68 parasitic draw problem. It really sounds like this is the issue from a quick review. Glad I typed it out.
You might have another problem but check the wiper solenoid issue first. Not sure I understand your statement about everything having power. The starter post, horn relay bus, and alternator will have 12 volts.
"Everything" is all encompassing so not sure what you mean.

https://www.corvetteforum.com/forums...post1607052246

 

thank you everyone for your responses. In response to everything having power, is it common that power will be sent to everything in the engine bay without the key turned to the run position? Like if the car has been sitting for ~2 weeks with no key in it and you pop the hood should the alternator, relays, starter, wiper motor, ac ect all have 12 volts of power to them?

 

The reason I mentioned the grounds is from my own experience. I was working on my '68 and leaned into the hood support and got a mild shock. Touched the throttle linkage to check full advance and got another mild buzz. I took my tester and found voltage all over. Cleaned up all grounds from the battery to the engine and it disappeared.

This reminded me of an event many years ago when a customer car came back from the paint shop with electrical troubles. In my trouble shooting I touched the body with a tester next to the battery ground and it lit up. The paint shop had painted the ground connection and after I sanded it back to bare metal everything was right again. Start with the simple stuff. Basics.

 

The ground connections on a C3 are always a "good place" to look! The most common culprit for draining the battery has been the windshield wiper "override switch" under the right hand side of the drivers area. If it is left in one position it will provide a constant drain on the battery until the battery goes dead. It is the little **** that turns to "over-ride" the wipers and allow them to stop so you can replace the wiper blades

Another common place for this to happen is the alternator's "bridge diodes" used to convert the AC to DC voltage. If one of them goes bad it will drain the battery as well.

My 1968 C3 is number 2595 and it does not have any "lights" in the rear compartments in my Convertible. Were these lights inside the three tiny compartments or was it for the rear deck under the cover? Was it a Coupe thing?

The reason the dashboard and accessories all have power is because your Fusible links are still working fine. They are located near the starter motor and appear like little rubber barrels on the outside of the wire. I believe they get their power from the Positive cable post on the starter itself.

11.1 volts is a bit low but since the engine is "off" that shouldn't be too big a problem. When the alternator is running the voltage should jump back up to a normal level. This battery is nowhere near full so it should be charged quickly in an effort to save the storage capacity of the battery. I would suggest that you isolate the battery and charge it completely (until it starts gassing). 12.2 is low for a newer battery and it sounds like it needs a good charge to help protect the battery. A new (er) battery should stay up around 12.6 volts so charge that bad boy!

Yes, when the battery is in the car it will send voltage to the accessories. Do you still have the original type of alternator on the Corvette or has it been upgraded to a higher amperage unit? Many people change the charging route when they upgrade the alternator in a 1968 C3. On my C3 the alternator output goes directly to my Starter 12 Volt post and from there the power goes to the battery itself. Then power is sent to the Horn Relay not far from the voltage regulator on the drivers side.

While you have the battery isolated from the car take a Multi-meter and measure the current being drawn into the vehicles electrical system. This is done using the negative cable of the battery with the meter set up for reading Amps located in between the car's electrical system and the battery negative post. Please tell us what it reads so we know just how big of a drain you are dealing with here. Harbor Freight has little devices that plug in place of a fuse and tell you how much current is flowing on that particular circuit. The meter in between the car and battery is the best way to identify battery drains. Depending on the meter be careful not to exceed the capacity of the meter you are using, many are rated a 10 or 20 amps and then they pop a fuse inside the meter which can be a PIA to replace.

Once the battery and meter are hooked up to read amps and are in place, pull a single fuse at a time and see if that circuit was pulling any current. This is where the HF tools come in handy as you simply put them in each fuse spot and test that circuit, when you find current "flowing" then you will know where to look.

P.S. Whatever you do Don't use any Die-Electric Grease on the Corvette. It sounds "conductive" but in fact it is not conductive! In the electrical system it can make some huge problems if used the wrong way. People have used in between connections and wonder why they had issues. One guy used it on his battery connections along with his ignition system and he really had some work cut out for him cleaning it up.