1977 K30 draining battery

Hello everyone please forgive me if this is in the wrong section I’m new to all of this! Anyways, my fiancée has a 1977 K30 (will attach a picture below) and the battery is having power pulled from somewhere and i don’t know where to start. I believe the alternator was replaced a year or two ago, in the fall her father put a new battery in and a killswitch on the battery and then had it on a tender all winter. We moved it to my house, the switch was off (not on the tender) and the next morning the battery was dead. As far as i can tell no lights were on and the interior is pretty bare bones as it came. How do i go about trying to figure this out properly? Any garage that was willing to take it was trying to charge me hundreds just to diagnose it. Thank you!

1) Is the replacement a one wire alternator?
2) voltage gauge or idiot light?

The simple start:

(1) Charge the battery.

NOTE: Don't let a battery get and stay discharged for long, because that causes what is called sulfation That is material forming on the plate and ending or at least reducing the battery's life.

(2) Disconnect the ground.

(3) Put a 12 volt test light between the ground cable and the negative terminal of the battery.

(4) If the light is on, something is completing a circuit, running down the battery. That could be a clock or radio, so you might want to disconnect it/them at the start of your tests (note where they go).

(5) If you want to be sure the test will work, and if the light is off, pull you headlight switch to an on position. The test light should light.

NOTE: Keep in mind, it only takes dropping a bit of power across a circuit to drain a battery, in time. As such, ONE of the most critical tools to have in your tool box is, a multimeter. It will detect and reveal what you cannot see with the test light.

(6) Start pulling fuses and watching the test light [or meter] until the meter no longer registers voltage or the light goes out.

(7) Don't forget there may be cobbled circuits from previous owners. They may or may not have fuses. If you're still showing a drain after pulling [and putting back] fuses, do a bunch more searching.

NOTE: Extra hot lines from the positive battery terminal or starter can give clues, if the simple tests don't give results.



OTHER SIDE NOTES:

* Years back, I worked on a car with a battery that was draining. The first thing I noticed was, the battery was filthy.

On a whim, I put a volt meter across the top of the battery and got about 12 volts. The dirt, debris and acids from the battery gassing mixed and produced a circuit.

I washed the top of the battery with a water and baking soda mix and the problem went away.

* My 78 battery kept dying in just a few days. The previous owner had wired the choke straight to the battery.

My friend Dave had this happen on his GMC shortbed square (early 80's model) - it was something in the alternator. Disconnected the alt and it started up just fine after sitting for weeks, with the alt connected it was no-go in a couple days.

YakkoWarner said:

My friend Dave had this happen on his GMC shortbed square (early 80's model) - it was something in the alternator. Disconnected the alt and it started up just fine after sitting for weeks, with the alt connected it was no-go in a couple days.

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Yep, had that happen a time or two. Once was just recently. I've also had a bad starter drain my battery before too.

Once thing to note with the test light method is that some things like a radio memory, or a phone charger in the sig lighter, will cause the bulb to light up very dimly. That should be considered normal and will not kill a battery in a week or two.

First thing disconnect the alternator completely. A bad diode will cause a draw. Next thing take a DMM in DC Millivolt Scale check voltage read at each end of the fuse,red lead on one end,black lead on the other. With everything off,no key in the ignition. If any fuses are showing .05 MV across them everything on that fused circuit is suspect,start removing those items from the equation.

Well your fiance has great taste in trucks!
What all these guys said ^.
Plus, much easier with a multimeter as suggested. Can look it up, but iirc anything over like 40mV is considered a significant parasitic draw.
The 86 has about that and battery takes about 2 months to die.
The 77 and my old CJ5 by comparison are both dead zero with a 1-2mV if you watch it long enough. Those can go forever without charging. Sometime I forget about the jeep for 6 months and it starts.

Dead in a day and disconnected?
Thats semi impossible. Has to be something hooked to the battery. With a significant draw.

Grit dog said:

Dead in a day and disconnected?
Thats semi impossible. Has to be something hooked to the battery. With a significant draw.

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Technically the battery itself could have some internal damage and draining between the cells - I have seen that happen especially if it gets bounced around or handled roughly. Normally you wouldn't even be able to get it to take a charge in that circumstance though.

YakkoWarner said:

Technically the battery itself could have some internal damage and draining between the cells - I have seen that happen especially if it gets bounced around or handled roughly. Normally you wouldn't even be able to get it to take a charge in that circumstance though.

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Hence the term “semi” impossible. To keep folks from saying “technically it’s possible.”

So, I missed that part in the beginning.

If you have a fully charged battery that will start a vehicle, then it gets disconnected and it will no longer start said vehicle after a day or two... that's a bad battery.

Semi, technically, or whatever you want to call it, that happens often. It has happened to me a number of times in the last several years. Battery quality is not what it once was.

I would advise taking the battery to an auto parts house and have it checked, alternator too, it’s free. Knowing the state of those first would help for starting out your troubleshooting steps

Ok, good points, could have a bad “new” battery. Or could have some stuff wired up that he don’t know about?

Grit dog said:

Ok, good points, could have a bad “new” battery. Or could have some stuff wired up that he don’t know about?

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One would ASSume that the OP would notice if there were other wires still hooked to the battery when they disconnected the battery cable.

I bought a car two months ago. It had a battery drain issue, when purchased. I know the PO, he put a new battery in the car in November. I fully charged the battery with it out of the car. It load tested fine. Then the next day, it load tested very poorly.

Same thing not too long before that. I bought those ambulances in July or August. I bought a new battery for one to get it home, and wound up using that one to drive everyday. After a few months it started going dead in a few days. Then overnight. Then in a few hours. After removing the battery and properly charging it, it spectacularly failed a load test.

Most likely a coincidence, but both of those batteries were purchased from O'Reillys. And they were both the "gold" or whatever the better ones are. Not the super cheap ones.

I do not read that that the battery was disconnected,and have doubts that it was.