intermittent electrical issue killing batteries.

[aggiegrad]

Looking for ideas on where to look for the issue. I have a 68 GMC that I still drive almost every weekend for the past year. It was a daily driver for about 3 years before that until my son left for college. Recently it has started to kill batteries. It never acts like it has low battery until one day I go to drive it and there is absolutely nothing. It checks at 4 volts and wont recharge. This was an AGM type battery and was replaced with another AGM battery. I checked for draws when I put it back in and had no draw and everything seemed normal. I continued to drive it on weekends without issue until one day when it did the same thing again (4 volts and want recharge). Thought maybe it was something with the AGM battery because I have run the batteries down before and never had one that couldn't recharge so I switched it for a regular lead acid battery and everything checked out and drove it on weekends without issue until it did the exact same thing this weekend. Now I know it is something in my truck that intermittently is killing the battery but not sure where to look. I haven't replaced this battery yet as I dont want to kill another one but I cant think what is intermittently doing this while it is parked. Has anyone had a similar issue or knows any way to find an issue that is normally fine.

For information it is still fairly stock and still has the external regulator. I have not made any changes to it for a few years. I did add headlight relays, a retrosound radio and switched it from lights to gauges and switched from amp to a volt gauge about 5 years back but none of that ever did anything like this.

Again looking for ideas before I lose another battery in 4 to 8 weeks.

Bryan

[Sheepdip]

Check and certify that you alternator, charging system and amperage requirements are up to the task. Example..If you are producing 70 amps with the alternator and consuming/using/requiring 85 amps your battery eventually goes dead.

[MySons68C20]

Originally Posted by Sheepdip

Check and certify that you alternator, charging system and amperage requirements are up to the task. Example..If you are producing 70 amps with the alternator and consuming/using/requiring 85 amps your battery eventually goes dead.

The Optima will die quick if the alternator is charging at to high of a voltage.
I used to have a Taurus that was putting out over 16 volts and it did the same thing.
Check your charge voltage....should be around 14.2ish.
Also, the new battery chargers won't charge a battery if the voltage is under 10 iirc.

[Steeveedee]

How are you checking the draw? Try pulling a cable off the battery and putting a test light in the circuit. If it lights, you have a draw somewhere. If so, start pulling fuses until you find the culprit. Also, if your ignition switch is old enough, you may be able to get the key out in the accessory position, which will run the battery down over time.

[leftybass209]

As Steeveedee said, you essentially need to trace the issue. You can use a tester, or a multimeter. Disconnect the negative cable, then use the multimeter in line to test the voltage draw.

[aggiegrad]

thanks for the replies. I guess my issue is that it seems to be an intermittent issue that is not there when I replace the battery. I check it with a multimeter inline between the battery and cable and have no parasitic draw. This is also confirmed that the battery will stay fully charged for more than a week between starts for several weeks in a row. This is the case for about 6 weeks until I find it completely dead after another week to 10 day gap. A draw that is dropping it to 4 volts and killing the battery would not allow the battery to stay charged that long between starts for that long without at least appearing low. I can even allow it to crank for a while as the gas has usually evaporated in the carb.
That is why I know it must be intermittent issue but I am not aware of items that do this intermittently.

If there is no parasitic draw when I put the battery back then I can not trace the cause. Just looking for other things people may have seen to cause an intermittent issue. I have the original wire harness which I realize could be causing it but dont really want to replace it unless I knew for sure that I would solve the problem. I am also considering replacing the alternator with a 12si but I have not heard of diodes causing intermittent draws.

thanks for your ideas

[HO455]

You might check your ignition switch. I had one that would occasionally catch, not quite completely in the off position. The engine would stop running but the accessories would still be on. I noticed it because I could hear the heater fan running. I had to be careful when turning the key to the off position until I got the switch replaced.

Another thing to look into is a corroded dome light switch that is partially grounding sometimes when the door is closed. It may be grounding just enough to make the bulb glow but not actually light up. And it may not happen every time the door is closed.

[Rust_never_sleeps]

sounds like a sticky relay. You prolly have to lay the mm on it to check it for drain every time you shut it off and then trace it when it's actually exhibiting the problem.
Intermittent faults suck, sorry

[PbFut]

Where are you pulling the voltage guage + from?. Guage match multimeter? If a relay is sticking you would probably notice the device it is for running. As said before, overcharging possible but you should see on the volt guage you added. For some reason the voltage regulator is popping into my head. That kind of supports sticky relay idea as I think the ext reg has relays in it.
Be sure the jump wire from +battery post to + block on fender has a fuse link on it. The harness is unprotected without the fuse link.

[aggiegrad]

Originally Posted by PbFut

Where are you pulling the voltage guage + from?. Guage match multimeter? If a relay is sticking you would probably notice the device it is for running. As said before, overcharging possible but you should see on the volt guage you added. For some reason the voltage regulator is popping into my head. That kind of supports sticky relay idea as I think the ext reg has relays in it.
Be sure the jump wire from +battery post to + block on fender has a fuse link on it. The harness is unprotected without the fuse link.

The gauge on the truck does not have enough precision as it just shows 13 and therefore is more a relative check. It is possible it was overcharging while I drove on the highway and didnt notice. I will keep a better eye on it when I drive it next. Also, the truck did not have a fusible link when I got it and was concerned. I had run a breaker (30 amp? if I recall) in the main line to the battery from the harness. Not sure if that could be killing battery if there is an intermittent short and the breaker keeps resetting. Just guessing here. I dont have time to get the battery replaced and check everything out do to many other higher priorities in life right now but I will let everyone know if I find anything.

thanks,

[MikeB]

Originally Posted by aggiegrad

I check it with a multimeter inline between the battery and cable and have no parasitic draw.

Is your meter configured to measure current or voltage?

[Rust_never_sleeps]

Originally Posted by MikeB

Is your meter configured to measure current or voltage?

You'd want to measure Amperage for this

[don t. - 72gmc]

I've had so-so success bringing a wet cell batt back to life.

Check water level, fill if needed. Keep caps loose.
Trickle charge for 10-15 minutes. Meter might not move. Watch for bulges in case, case getting warm.
Turn off charger.
Repeat until charger meter actually shows a charge.
Might take a day, maybe a week, before I was able to fully charge the batt.

I had time, doing project near by, when trickle charging.

Common sense applies. Had 1, case started to bulge. It got replaced.

HTH...good luck...Don.

[dmjlambert]

Does your horn work normally or do you have it disconnected? I ask because it is common on these old trucks for people to disconnect the horn because it blows intermittently due to cracked up original steering wheel or poorly designed button-works on an aftermarket steering wheel. The horn relay would then be a problem.

[Sparky dave]

A quick check to see if you have something pulling the battery down when parked. Undo battery terminal and touch it on battery, if you see any size spark it has current draw in it. Then move to fuses, same again pull them out and in , any spark you have draw down on that circuit and can investigate further.

[MS66]

First thing to do during the time you're diagnosing this problem is to disconnect the negative cable when the truck is not in use. This will save your battery.
It sounds to me like it's the diodes in the alternator, or possibly the regulator. Best thing I ever did to these old systems was to go with the later version, internally regulated alternator. If you want to keep the external regulator, get the solid state replacement version of the external regulator. It works great, I actually have one on my '68 that has the original alternator still in it.
There are a lot of good replies in here already. You should be able to pin point it. Sparky dave put up a real simple way to detect current flow, and I have used that when no other tools were available to detect current draw.
Check your body ground to frame under the cab.

[RichardJ]

From "myson68 " above;
>>Also, the new battery chargers won't charge a battery if the voltage is under 10 iirc.<<

Some chargers have a work-around in their instructions that can help you trick a charger into starting the charge.
A good battery connected in parallel with a dead 12v car battery can trick a charger into beginning the charge. A good battery can be another car battery or even a small 9V battery. You just have to momentarily show the charger that there is a battery connected. It should then begin to charge and continue after the extra voltage source is removed.

A 12V test lamp between the battery and the battery cable is very reliable, but better yet is a analog Amp meter or analog multimeter. Digital Multimeter Ammeter take a reading, then display and then wait a second to take a new reading. With an intermittent problem you can have the display numbers dancing around and providing no real information.

I had a similar battery drain problem in may Corvette years ago. Who knew factory power antennas had a internal, self-resetting circuit breaker.
12 v test lamp, digital voltmeter and digital ammeter readings gave me no useful info. This 20 Amp meter gave me the info I needed. After watching the meter for several minutes, I was able to see what was going on and when.
This is now my go-to for any automotive load testing or battery drain.

[aggiegrad]

Originally Posted by dmjlambert

Does your horn work normally or do you have it disconnected? I ask because it is common on these old trucks for people to disconnect the horn because it blows intermittently due to cracked up original steering wheel or poorly designed button-works on an aftermarket steering wheel. The horn relay would then be a problem.

Yes my horn works normally. Actually everything(all lights, a/c, all gauges, radio etc) works like it should which is why I was coming here for ideas. I am leaning toward an alternator and considering switching to 12SI. I am just wanting to rule other items out as I dont want to replace another battery. This is under warranty so I just need to get it replaced when I have time to begin checking things out. I will make sure there is no draw using the multimeter when I initially hook it up. Hopefully there is one so I can pin point the source.

Please check my reasoning on why I assume the alternator is the most likely scenario if there is no draw when I replace the new battery.
1)If is was the ignition switch sticking in ACC when I park it, the A.C fan and radio would continue to operate which would be obvious.
2)If the headlight relay stuck, I would think the headlights would have stayed on. Obvious at night in driveway

[MikeB]

Originally Posted by aggiegrad

Please check my reasoning on why I assume the alternator is the most likely scenario if there is no draw when I replace the new battery.

I've never heard of an alternator having a parasitic draw on the battery. But I'm not familiar with external regulators, having converted my truck to a 12SI alternator many years ago.

But if you think that may be the problem, can't you simply unplug it to see if that stops the draw on the battery?

[DLH]

Get a thermal camera now that it is cool out and look for warm wires, circuit boards, alternator etc...anything glowing is using power.