89 coupe- just started a couple days ago, battery has been strong- it was down to 10.4 the first time, driven the night before, didn't find any of the usual reasons for drain, charged it, started it 10 times, battery came right back to full voltage quickly each time. This morning it was almost completely dead, disconnected the battery and it was at 6.8v, and it came back up to 8.4 within 10 minutes of the disconnection, so it doesn't seem to be the battery- put the charger on it with cables disconnected, and it came right back up, and seems to hold it's charge just fine if disconnected. Console light, hood lights, courtesy lights functioning correctly. Just went through all the usual tests, have my DVM between the neg cable and bat terminal, showing constant 77ma draw with courtesy light fuse out, pulled all the fuses and breakers 3 times, never a flicker in the needle, and removed the pos lead to the fusible link feed terminal behind the battery, which should disconnect all the circuits, and again, the needle never flickered- still a steady 77ma. Are there any other circuits, fuses, breakers, etc. other than those in the fuse block and the terminal behind the battery? 77ma might possibly be within the range of error in the DVM, but it is going dead overnight, and the meter has always been pretty accurate

 

Do you have an aftermarket radio? I have had problems with 2 . 1 was a motorized faceplate, the other was an in dash cd changer. th cd changer was in the vette and would drain in a day or so. The radio was in a Z71 and would drain as well just not as quickly. I would start by removing all aftermarket items..radio, amp, and etc. If you have it.

 

I believe that the spec drain is around 50ma(your clock radio will always draw a very small amount of current). After you charge your battery up, the surface voltage should be between 12.5V and 12.8V(engine off, all accessories including interior lights off). Anything less than 12.4V is considered discharged.

Your battery voltage at idle should be between 13.6V and 14.3V. This is the voltage generated by your alternator.

If a 77ma drain is causing your battery to go from fully charged to 6.8V, I would suspect that you need a new battery. Take your battery to Pep Boys or Advance Auto and they can test the battery with a load tester.

 

If you go back and read my post, all that general charging system stuff that is pretty much the same for all 12V vehicles was addressed- and I was working against the spec of 50ma from the shop manual. The battery is on the charger now, unhooked from the car, about to be turned off and checked for V, and re-checked in the morning, to see if it holds a charge. I wasn't looking for general automotive stuff, just 89 Corvette-specific stuff- like any circuits other than the ones I've checked that could be draining it. The radio is aftermarket, but is wired through the key, but I plan to unhook it next, see what happens. I'd really not like to buy a battery if not necessary, as I have no other use for one of GM's worst ideas, the side-terminal battery

 

OK got it. I guess I was looking at it from the standpoint of a 77ma drain, taking out a battery overnight which is capable of churning 700-800CC Amps. 77ma versus 50ma is not a big delta and your battery should be capable of handling this without a problem.

 

If jfb doesn't respond, send him a PM. I think he drives an '87, and is the best "electrical guy" on the forum. Always eager to help.

 

If no fuse removal had an effect on the leakage current nor removing the wire going to the jump start bolt behind the battery, this still leaves a few circuits you haven't disconnected. The starter motor for one, it isn't fused at all. If you have the 89 electrical diagnosis book, look at the power distribution page very early in the book, it shows all the electrical power distribution and where the fusible links are located. There are three fusible links that are not on the jump start bolt in my 87 and I think its the same for 89's. One goes to the aux cooling fan relay. One goes to the coolant fan relay, and one goes to a splice supplying power to:
1. Oil pressure switch.
2. Fuel pump relay.
3. ECM.
4. Mass burn off control relay.

My money is on the ECM as there are some electronic components that have 12v on them all the time like some IC voltage regulators, electrolytic capacitors.

My 87 manual shows connectors on all 3 fuseable links, so if you can locate them you can disconnect them while watching your ammeter.

Also, car batteries are considered discharged when their no load terminal voltage is 12.0 volts or below and fully charged at 12.9 volts and above.
If you need descriptions of where these fusible links are I have access to the 89 electrical diagnosis book and I can either scan it or describe the locations to you.

 

Thanks, yes I have the shop manual, got to where I'm at from there, just need to track down the other circuits. Actually, when I connect the ground cable, I can hear a click down front, maybe the fan(s)- is it normal to hear a sound from the relays at hook-up, or a clue?
Battery was at 12.88 when I pulled the charger off 4 hrs ago, and is now at 12.45, disconnected from the car- not a good sign. I'll see what it reads in the morning, if it's gone down much more, off to the store Didn't seem like a battery problem as it spun over fast and started great 10 times in a row yesterday after charging- we'll see if it goes down tonight. I've never done the "shotgun" approach, try not to buy parts until I know they're bad- especially something like a side-terminal battery that I have no other use for
If it was reading something like 300ma, I'd be pretty convinced there was a problem- 77ma, getting down to curly hairs- but it does throw a pretty good initial spark when hooking up the ground cable, a little more than I'd expect, or like, to see- back to work on it tomorrow

 

Although 77 ma is out of spec as 50 ma is the limit, a normal current drain is usually 25-35 but closer to 30 ma. My car draws about 29 ma and can sit for weeks with no problem. So twice the current drain (77ma) should have no problem at all with a couple days especially over night.

So either your current reading is somehow wrong, or the battery is bad. And even though a fully charged battery can look great right after charging, it can be near dead in the morning especially if the battery is at the 3 year mark and used in a hot climate. Down in Orlando I’m looking to replace any battery at the 2 or 3 year mark that even flinches the wrong way and has any signs of not being right.

You can cut to the chase of this problem real fast by charging the battery up but don’t connect it to the car. Then the next day connect it and see if it will start. That will dam sure eliminate the car as the problem if it does not start.

Best to fill you profile out.

 

You shouldn't hear any clicks or any other noise when you connect your battery up. Also I agree with pcolt94 that 77 ma. drain will not discharge your battery in the short time you experience. It is also normal for battery voltage to drop after disconnecting a battery charger and your numbers are normal. When you measure battery voltage to determine the state of charge you are supposed to let the battery sit for 24 hours disconnected after charging. As batteries age their charged up voltage drops from the 12.9 or higher that you will see with a new battery. Sitting disconnected and starting fully charged you will see a very small drop voltage drop each day, like 10 to 20 millivolts, if you see .1 to .2 volts, you likely have a battery near the end of its life or one with excessive internal leakage current.
Look in your electrical diagnosis book and find the three fuseable links in the power distribution diagram that are not connected to the jump start bolt and then look up their location. At each location it is possible to disconnect by unplugging a connector, do so while looking at your ammeter.

 

Thanks, jfb, the other circuits are what I was looking for, have to spend a little more time with the shop manual
Just checked it after 15 hrs, and it hasn't changed, still at 12.45, seems to have stabilized at that point from the surface charge. It's about 50 degrees outside, so it shouldn't be losing a lot to temp, probably at 75-80%- not as good as I'd like to see, but not shot either. I hooked it back up, and it went to 12.31, and after 45 min, at 12.33. I just unplugged the underhood lights so I could leave the hood open, and replaced the courtesy light fuse- it went to 12.12 while the interior lights were on, and then came right back to 12.33 when they went off- I'll check it again in an hour. OK, still rock steady after another hour at 12.33- not real strong at about 70%, but should start the car, and sure doesn't seem to be discharging anywhere near like it was to get to 6.8V- everything is hooked back up except the underhood lights, and I had confirmed that they, and the glovebox light, were shutting off correctly with their mercury switches- but never say never with electrics...I can try it with a known good, same-size battery by bolting some normal battery cables to the sidemount cables and setting the battery next to the car if I have to, see if it runs that one down- but right now it doesn't seem to be discharging . What sounds like a relay clicking up front seems to be coming from the headlights, should there be a cycling to "normal" when the battery's connected, or should that jump to the top of the list of circuits to test? I'm going to go thru the cables & grounds again to be safe- everything I've looked at so far was clean and tight, and cleaned them anyway

 

No clicking anywhere on the car when you reconnect the battery! Also, courtesy lights on, dragging the battery voltage from 12.33 to 12.12 tells me you have a battery at the end of its life, it needs to be replaced! Its a door stop now. Measure the battery terminal voltage during cranking, it should NOT fall below 9.0 volts or its discharged, or at the end of its life!
77 ma. could only be within the meter's accuracy tolerance if you have it at a very high full scale range.

 

Here is just a tid bit of information from my personal experience that pertained at least to my 94 car. When I initially went to get the current measurement several years ago, I could not get a good reading while trying to use the lower scale of 300 ma on my meter. I was getting false reading and low measurements as the cars systems and computers were just not coming on line and getting to the initial power up mode as would be normal.

When I made the same connections trying to get the measurement again but this time using the 10 amp scale, the car and all systems came up properly.

The problem was that the different scales on the meter has different internal resistance thru the meter. The higher scale allowed the car to power up correctly as if the meter was not in line. Obviously there was too much drop across the meter on the lower scale. At first connecting of the battery, the systems probably need additional current, and then the current falls off to the normal. It’s just with the higher scale I could not read to the right of the decimal point.

I have no idea if the earlier vettes have this condition as I did (or other 94s). This was my car and meter, different from everybody else’s. But it is just a thought to consider as it may or may not pertain. Perhaps another meter might work different.

* When my battery is connected my headlights click also which is normal. If this does not happen when you connect your meter in, then the car is not powering up correctly.

 

Yep, I agree the battery's not very strong, still strange that it's not discharging now, it's about 65 outside now and it's reading 12.36 after another hour. Always possible that there was a connection problem in the cables that got fixed from the cleaning, but everything was clean, bright, and tight. I think I'll check the car with a known-good one, I have one the same size to use, just have to rig up some cables- too bad I can't just put it in the car- I'd love to talk to the rocket scientist who came up with the side-terminal battery Just don't want to buy a battery until I'm sure I need it, and I'm not in a hurry- and of course, they didn't punch the date on the battery, and there's no record of purchase in the file of receipts- and it is an Interstate LOL Gonna leave it hooked up overnight and see if it drains down again

Thanks, Gents, I'll let you know what I find- gotta get back to work on that customer 428 Cobra Jet stroker engine

 

You could save yourself a lot of time by taking your battery to just about any auto parts supplier and have it load tested.

Is your charging system working properly? The alternator is another battery direct connect component that is hot at all times. Bat voltage is always present at the cathodes of 3 diodes of the rectifier bridge, and if one or more of these are leaky, this can add to constant battery drain.