im in the process of getting my 75 c3 on the road. i have just installed my third new battery in the car. so far i have not taken it out of the driveway. i rarely leave the battery connected after the first new battery went dead . today i was planning on taking it at least around the block , but the battery was dead again. the auto parts store says it must be something wrong with the car and will not replace another battery. so my question is why.
i understand that a battery can go bad if it is idle for too long, and that a significant drain will deplete the battery, but shouldnt that be fixed with a slow charge. if there was a bad drain on the battery shouldnt there be at least some arcing when attaching the battery lead? also i dont see any problem showing up on the charging guage. . the only drain should be the electric clock whidh is the updated quartz one. nothing else should be actively draining the battery. should it?
thanks in advance for any help.
im installing the new battery tomorrow, and will try to test for a current drow, but i don[t think my vom i made for high amperage readings
i did a search and couldn't find answers. maybe i didn't know how to do that either

 

Not certain just how long it takes for your car to drain your battery.
However, here's an example from my 77.
I drove it to L.A. several years ago. the route I took was well over 4,000 miles. So I believe the then 3 year old battery was fully charged. They loaded my car into a shipping container.
I flew away to the other side of the planet.
After a few weeks the sealed container was finally put on the world's slowest moving ship. The ship then went off to 2 different ports in China, then finally headed off to Australia.
the car was sealed inside the shipping container with the battery connected for a little over 4 months. I met it at the docks. Hopped in and the clock still kept perfect time. (just that it was set on California time). Turned the key and she fired right up. And no, it didn't even turn slow.
About 8 years later that 2 year Walmart battery finally bit the dust.
Soooo, I'm thinking you have an issue. Bad diode in the Alternator is a common cause. Could be a number of things.
Do you know how to do a Mili amp draw test?

 

Just to make sure I’m getting this right, are you sure the car is charging the battery while it’s running? And that the battery is fine if started frequently but if it sits for a while then it dies?
If you haven’t already, check and make sure your alt is putting out 14+ volts. If it is and it’s charging right, then I would think that you have a draw that is draining your battery. As mentioned above. Diodes in the alternator are common cause.
If you have is a standard volt/ohm/amp meter with leads, just connect the amp meter, in series, between the battery positive lead and the positive terminal(car off). The meter will show what amount of current is flowing between the two. Be aware that having the doors open, will turn the interior light on and that will show as additional current. Standard meter has a 10amp fuse.
if you disconnect the regulator circuit from the alt; you can redo the measurement and compare.
Essentially you can continue to disconnect various larger circuits until you find the draw.

 

First off let's talk "bad battery", just because a battery is low on voltage doesn't mean the battery is bad and needs to be replaced. Sounds like you have is a parasitic battery drain. Take a cruise through the below thread on the subject.

https://www.corvetteforum.com/forums...aw-help-2.html

 

A side note. Just because a battery went dead, doesn't mean it can't be charged up again. I have had batteries die because lights were left on, charged up and last for years after that. This sounds bass acwards but I would check all of the frame contacts for the battery and starter cables.

 

Just did this myself. I needed to get an amp meter that would not blow a fuse easily. Probably needs to be a digital one that is able to measure DC amps of at least 10a but 20a would be better. Bought an Innova mid price range for about $30 something dollars that works well for automotive use. You could step up to the $100 unit that does a few more things but it also requires extra accessories to make those functions work so I passed.

Disconnect the courtesy lamp fuse first and then the negative battery terminal. Put the meter in the high amp measuring mode. Touch the black lead on the meter to the negative post on the battery and the red meter lead to the loose end of the negative battery cable. If you read more than 50 miliamps draw (.050 A), you have a parasitic electrical drain somewhere. I had .2 A draw which is 200 miliamps so I knew I had a problem.

Started pulling one fuse at a time and rechecking the amp draw. If it did not change, I put the fuse back in place. Just kept pulling the fuse and rechecking until i found the culprit. In my case it was in the alarm circuit. I dont use it so, i just left the fuse out. No more parasitic drain!

Hope this helps.

 

First, get a battery quick disconnect, if you aren't fond of leaving a tiny wrench in the car and disconnecting the terminal each time.

I've left a battery (disconnected) in a C3 for 6 months, reconnected, and fired up. So time is not the issue, your parasitic drain is the issue.

Do you have a multimeter and know how to use it? Do you have a battery trickle charger to at least offset the drain until you can find it? YouTube might be the best way to learn about this, rather than a bunch of words thrown at you with no context or pictures.

If you check all of the normal circuits by pulling fuses one at a time, and still can't find the drain, a popular location is a failed diode in the alternator.

 

Pro Tip
When chasing a wiring problem on a 40 something year old Vette instead of using the 12V car battery use a 9V battery (solder +/- leads with clips to the battery), will help you from melting wires as you troubleshoot.

 

Welcome to the forum. My money is on a weak alternator

 

My battery also went dead and it looks like the "glove box" light was likely the issue for me. My glove box was not latched shut and the spring loaded light switch can push the glove box open enough to turn on the light.If you have a glove box light, make sure it is not staying on.

 

first, thanks for all of the advice. i especially liked the one about using a 9v battery. great idea. i hooked up an ammeter and found a 3 plus amp drain in the brakelight fuse. on my wiring diagram this leads to a sequencing unit. i ran a search on this forum for more info, but gave up looking after sifting throught the first 50 threads.
so now i know that there is a serious problem, any clues on where to look?
also i mentioned that i have killed 2 previous new 3 year batteries. what i should have said is they could not be recharged, either with a slow charger or a fast charger. i understand that a parasitic drain will delete battery performance, but why does this drain kill the battery?

 

Is the 3 Amp drain the only parasitic drain? That's a lot. Hopefully you can find it and fix it.

Standard starting batteries cannot be deep discharged. If you fully drain all of the charge out of a sealed lead-acid battery, it will probably never recover.

In modern cars, there are often protection circuits to prevent this. Not so on an old car. It is as if you connected a 4 ohm resistor across the battery terminals and left it there until the battery was stone cold dead. That's why I suggested a battery cutoff switch first.

 

Pulling a battery down to totally dead, DEAD. is not good for a battery. I have seen this kill a battery many times.

 

battery issues now understood, thanks. can anyone help with the sequencing unit. where is it, what does it do. etc

 

When you hook up the NEG cable, there is usually a spark let you know something is "ON". Clock doesn't draw enough to warrant a spark.
To keep the dome light off, jamb a stick between the front of the door jamb and the door jamb button.

Besides a bad ALT diode, some model yrs had issues with windshield wiper relay, which would put a constant parasitic draw on the Batt.
Don't know which yrs.

There is a special tool that grasp the glass fuses and pulls them w/o breaking. It can be found at automotive stores.
Be prepared and have spare fuses of every Amp.

If you find a circuit with a draw, leave the fuse out of that one for now and continue testing the remaining circuits There could be more than one faulty.

 

You need to isolate the battery and figure out the source of the parasitic loss your battery is being connected to. Many people are not used to doing this but I always recommend that you charge a battery completely before installing it in the vehicle. You want to push the Flooded Lead Acid battery up to 2.50 volts per cell minimum which works out to 15 volts DC on the battery and this is done to have the battery completely charged before using it. I personally even discharge the battery 80% and the recharge it two or three times before putting the new battery in the car. Any FLA battery that has been sitting on the shelves for a few months will likely need a good charge before being installed anyway. The idea is to get the battery to the gassing point ~15 Vdc to ensure the electrolyte is well mixed up and not stratified.

Once you install the battery in your Corvette measure the voltage and watch it for a day or two to be sure the battery doesn't have a overly High Self Discharge rate which is killing it. A new FLA battery should self discharge at about 1-1.5% of the total capacity a month. This means it should have no problem holding 12 volts for a couple weeks without being charged and being disconnected from the car. The average FLA battery used in our Corvettes varies from 80-100 amp hours in capacity so they are able to hold a 12 plus voltage for several weeks. Once you know the battery is okay and not self discharging quickly then take a Multi meter and measure the current flowing across the negative terminal of the battery to the negative cable. You can connect the positive to the battery and then measure the amperage of the current being drawn on the negative leg. I use meters that have 10-20 amp measuring abilities and they simply go in between the battery negative post and the negative battery cable end. If you are seeing a 3 amp loss that is too much to leave alone, I would fix that issue before leaving the battery connected. Since you have a quartz clock the current should be somewhere around .2 to .3 amps at the most. If your C3 has the windshield washer override like mine does this can draw significant current if left in the wrong position. It is the round **** that stops the windshield wiper from moving when the cover is up because you pulled down the little cap on the override below the right side of the dashboard. I don't know when they discontinued this so you might not have the device.
Make sure there is not an alarm or amplifier that is on trying to pull power either.

If you discharge a FLA battery and leave it for any time it is damaged and can loose capacity very quickly as the plates will get oxidized and no longer function. This is why you never want to leave a FLA battery UN-attended for any long periods of time. If the battery is low on water in the electrolyte the same damage can occur leaving you battery with less capacity than when new. Small battery tenders that don't regulate can also cause the battery to boil away all the electrolyte causing the plates to be exposed to air and getting damaged. I remove the FLA batteries and keep them on a charge bench in my garage where I clean them add distilled water if needed and then charge them to 15-15.5 Volts ensuring they are fully charged. Keeping them clean, watered and charged is important to a long life for a FLA battery.

I am sorry that I can't help you with a Brake sequencing unit as I have never heard of one. If it has anything to do with the brake lights be sure the switch is releasing when normal so it doesn't keep the brake lights on. Dirty switches or broken springs can cause issues like that.

Best regards,
Chris

 

I've been working on these cars since they were new. never heard of this sequencing unit your talking about. Power out of brake light fuse goes to brake light and 4 way flashers.
I would suggest that if you remove the brake light fuse and the drain disappears. try removing the flasher unit for the 4 way flashers, located at the fuse panel. if that doesn't stop the drain then it's in your brake lights. Power goes to brake light switch, out of switch when depressed, into steering column to turn signal switch, out of signal switch by 2 wires to the turn/brake filament in the rear bulbs. That's it.

 

Does any wiring going to the proportioning valve? Asking for a friend.

 

Seriously?
Tell your friend. power comes from the "Guages" fuse. pink wire to the brake warning light. Brake warning light is NOT grounded. Instead, tan wire goes to connector S340 where its splits off 3 ways. One tan wire to switch on park brake lever. another tan wire to the ignition switch and the third tan wire to the brake pressure switch. These switches go to ground when activated.
So short answer . brake light fuse does NOT go to brake pressure switch. (what many on here refer to as a proportioning valve.

 

It shortens the overall life of the battery but with todays modern battery chargers Ive always had no issues recovering them myself. many even have a recovery setting on them which uses PWM to desulfate and clean the plates.. and this does often work. I use one on some 6 volt golf car batteries I have which are now 10 years old. I recently completely killed all 6 of them and was able to recover them in 2 days.