Good morning. This is an ongoing issue I've had with the car for the last couple of years. I thought I fixed it when I rebuilt the alternator but it seems to have come back.

basically, I can leave the car for three months sitting. And it'll be 50/50 if its charged or dead when I get in it. Every time I've done a parasitic draw test it's been showing around 25 ma. Which to me seems normal. It drops to about zero if I unplug the regulator on the alternator. My math tells me that should be 2 months on a standard battery to about 50% charge. That's all well and good but sometimes the thing can't sit a week or even overnight.

I've checked grounds, pulled fuses and done everything I could think of and can't make it not do this. I'm starting to suspect the instrument cluster but everything functions normally and it generally is a work o not type thing. Any ideas on what else to check is much appreciated. Thank you in advance.

A very annoyed Paul.

 

Alternator or creative wiring.

 

Wiring is all factory. I have my meter inline right now. The 15 amp clstr/clk fuse also runs the interior lighting so here goes.

once the lights go out, draw stabilizes at 35 ma. Removing the 15 amp clstr/clk fuse drops draw to 29 ma. Removing regulator plug from the alternator drops draw to 25 ma. Removing all fuses from the fuse panel drops draw to 23 ma. This sounds about right. I'm going to pull the belt and rotate the alternator and see if it changes.

 

Once key is turned to off there should not be any current flowing through regulator.

 

Isn't one wire straight to the battery and the other the charge light? (Sensing and field) And then the heavy gauge battery wire also?

I know it shouldn't but who the hell knows with old crap.

 

Pretty much there at 2 hot all the time and 1 12v with key on. A leaking diode is possible.

 

Okay, so according to my meter that accounts for a 3 ma draw difference. I've tried moving the column and messing with the ignition switch with no charge. Resting draw hovers around 28 ma eith it plugged in and the 15a fuse removed. Very strange.

 

starter ? had that on mine 84 !

 

I had a Fiero that would drain like that, turned out one of the headlight motors wasn't going completely down, so it was sitting wobbling from time to time - if it was in that condition it would drain the battery. I suppose Vette lights and convertible motors kind of operate the same way, open a relay when they're all the way down. It's a desperate suggestion ..

 

I do occasionally have to smack the wheel liner to get the passengers headlight down sometimes... interesting thought.

 

What Brand battery is it and how old is it? Your "Standard" old fashioned Flooded Lead Acid Batteries (FLA) can self-discharge at higher than normal rates near their end of service life. The easy way is to have it tested using a load like most auto parts stores have to test your battery. I like testing the battery by monitoring it for a few days measuring the voltage while the battery is disconnected from the world. Record the voltage and temperature every day at least for 10 days and it will show up if the battery has a higher than normal self discharge.

For cars that get less often usage I have found that the new AGM (Absorbed Glass Mat) batteries are really nice and unfortunately more expensive. Their "Self-Discharge" rate is much lower than the standard old FLA batteries but they are not really designed for the "Standard" way of charging batteries which are still using set-points developed for the FLA batteries.

The normal (automotive battery) set-point settings work great but they were designed for your FLA and can potentially over-charge a set of AGM cells. The car manufacturers have not come up with a system that can adapt to any type of the different technologies of batteries made today. I have seen brand new Lithium Ion Batteries that have been designed for car starting and ignition applications. They use another set of different set-points altogether. Batteries today not all "one type" and the different technology batteries each have specific charging procedures. Someday the car will need to know which technology battery is in the car so it knows how to get the maximum life out of the battery using the proper set-points and monitoring the temperature while charging.

For now, me and my family we use stand old FLA batteries, I have seen a lot of "Maintenance Free" batteries that were FLA batteries where they try to keep you from opening the cells up and adding to the electrolyte when needed.

My whole point is that try not to overlook batteries as they can wreak havoc when they get worn out.

Good Luck and I hope you have a Wonderful New Year full of great Corvette experiences!

P.S. For tracing drains like those the Harbor Freight offers a little automotive ammeter that shows the current going through that particular circuit, it plugs in replacing the original fuse.

 

I wouldn't be as annoyed if the battery weren't 3 months old. It's the advanced house brand flooded but still... I tried an agm on the boat once, the house charger has pwm charging and settings for battery types and it lasted no longer than a flooded one so I was out on those.

I have experienced crap batteries, that is actually why the car has a new one, I load tested the old one to 400 amps with a reserve capacity of about 20% of stated. Basically, it couldn't start the car with out a jump even when fully charged. But that was a bosch and apparently they fail right at three years as that has been my experience with them.

that harbor freight tool is pretty nice, I used to just solder wires to a burnt out fuse in line with my meter.

 

An old current shunt that is my back-up fail-safe. I have found that the most used tool is a Good quality Multi meter and second to that I use the Power Probe 4 that I have. The power-probe gets connected at the battery with a 15' long cord which lets you activate circuits and see what they draw. It will supply "Ground" or "Positive" 12 Vdc to the tip at the flick of a rocker switch. A Very handy tool on Corvettes and RV's of all types.

I am clearly off the mark suggesting it might have had something to do with your battery in this case but you would be amazed at the number of things an older battery can do. Your car has something drawing more than the normal typical parasitic loss for a C4. It will take time but you are going to have to check each circuit to find the drain. Start between the battery Negative post and the battery cable and document your testing. If you can install your meter (in the measuring AMP mode) in between those points it would be the best place to start. If you are not comfortable with doing this then don't, we don't want to hurt your Corvette or you.

I have heard of Starters having loose and or corroded connections causing the car to require substantially more cranking power to start, it is worth checking. You might want to have the starter tested to verify it is working properly, it could be pulling way too much power.. What is the loss when you disconnect the alternator from the battery? I have seen alternator's loose part of their Diode Bridge rectifier and cause them to use power.

Do you have access to one of the HF current meters? I would use a quality Volt Ohm Meter as it will give you accurate numbers and several can handle 10 amps continuously. Let us know what you have found when you have identified the culprit.

Happy New Year!!

 

Well that's just it, I have the meter inline with the ground and have a total key off draw of 28 ma or .028 amps. (The meter completes the connection to the battery from the ground) It goes up .03 with the regulator on the alternator connected. Using a 100 reserve amp capacity a 50% discharge at that draw is roughly 72 days... so like that's why I'm scratching my head. Right now it seems fine. But it isn't always.

 

Forget that HF tester. It can't measure current under 100 mA accurately, has no adjusting ****, and only fits one size fuse.
https://www.walmart.com/ip/Cen-Tech-...iABEgJ14vD_BwE

 

Same one at HF for 13.99
https://www.harborfreight.com/30-amp...ter-67724.html

 

Thank you cdm747 for the picture and the price of the harbor freight item. I use a Fluke 83 meter generally and it is very accurate but the H/F tool works great and is fast checking all the circuits. The meter is by far the most accurate way to measure the drain you re dealing with. Intermittent drains are the very worst kind to have to track. have you checked the post that is mounted on the frame rail where the fusible links get their power from the battery? If there was a lot of corrosion or a loose fitting that might be an issue. I would also check them for drains with your meter while you are cleaning them up. There are several wires attached to this post and on my 1988 C4 it is in between the battery and the front of the drivers door on a frame rail. On my car to see it I removed the cover with the gills in it covering the end of the battery. I had a ton of corrosion here, it is worth a check at least. I would test each one of the fusible links for drains while you are at it.

"I don't need no stinkin adjustment *****". "Keep it Simple Simon". The simplest tools are some of the best out there! I was surprised that Walmart was twice as expensive as the Harbor Freight price!

84 4+3, it sounds like your normal parasitic drain is within factory limits. Does your car have the built in alarm system? I am just thinking about the other potential places a drain might occur and alarms are a great place. Even more so if the alarm was added by a previous owner..

I would like to wish my fellow Corvette Forum Users a Very Happy New Year full of awesome Corvette Moments!

 

Happy new year to you as well.

I cleaned up the post when I swapped the battery. The one you are referring to. It was clean and tight so no dice there.

I believe the car has the factory alarm. I never lock the doors but I do have the flashing security light on the dash, doors open etc. The whole thing with the car is that the previous owner was a corvette guy so he mostly went through and fixed everything back to stock so theres is little to no after market writing on the car. The only thing that is is the clutch switch is jumped out, because the switch is nla. That's a 3 inch jumper. Other than that. I was thinking maybe the radio or something but again that wouldn't make sense.

One thing that I do remember is that way way back, when this first started happening, the passengers side mirror would go all the way out. That was always weird.

 

Just a few more numbers, my key on current draw is 4 amps after the fuel pump primes. That seems about right. Key off it drops to 1.2 for about 5 seconds then goes down to the 34 miliamps it has with everything hooked up. I'm going to drive it then see if I can get a different idle draw.

 

If you have the value of the resistor used in your ignition key there are companies that sell permanent disabling device for these pesky alarm systems. I would probably eliminate that device from your list by disabling it. The built in alarms have been known to be real trouble at times. I bought my disabling device from Mid-America. They are cheap, I paid less than $30 for the device and it simply plugs into the system under the dashboard

The passenger side Mirror goes all the way out? Is this after starting the car or when? That is something I would investigate as you might have a problem that could draw a bit of current if the switch continues to run trying to hold the mirror out as far as it can, that could eat some serious current potentially. I would disconnect the switch from the electric mirrors for a couple weeks and see what happens.

Good Luck and best wishes in finding the culprit who likes eating away at your battery!