Battery Discharge Problem

So I have been pulling out my hair with this problem and now it has left me stuck unable to attend my college classes…so hopefully I can get some insight or ideas.

I have a 1979 Toyota Pickup and a few weeks ago I noticed the charging light was comming on. So I took it to my local Scuck’s and they tested the Alternator and told me it was bad. I bought a new one, put it in and notice the charging light remained on. They said it was the voltage regulator. Got a new one put it in and discovered that it was overchrging and had the old one tested nothing wrong so put the old one back in, tested the charging sytem was told everything was fine.

Over time the chrging light went off… I thought everything was fine. The other day I was driving early in the morning to school and I turned on my headlights and drove about 30 miles to school and stopped at a copnveinience store to get a pop. When I came back out I tried to start the truck and it cranked really slow. Well, I was concerned the rest of the dat that it would not start so I tried to start it half way through the day and it fired right up. That night I began to drive home and I was using my headlights and about a mile from my house I turned off the highway and engaged my blinker and it did not work. I came to a stop and my engine started to spudder. I barely made it home, by the time I got home my headlights were extrememy dim, so I shut it off.

The next morning the truck started fine, so I went to a local grocery store about a mile away, went inside, came back outside and the battery seemed dead. No I did not leave my lights on or anything. I got a jump and it drove home fine but once I shut it off and tried to restart it…seemed like a dead battery.

This morning I went out and started it with no problem, shut it off and again seemed like a dead battery. So, since my school is 30 miles away I do not want to trust it anymore until I can figure this out.

The Alternator is new and I know the voltage regulator is working OK…and I read up on battery discharge problems… but none seem to fit this situation, do you think a closed circuit or a problem in my fuse block?

Any ideas would be muchly appreciated.

It could be an intermittent residual drain, which might be difficult to find, but first, what about your battary? How old is it? Did you have a load test done on it?

For $20 or so you can install a dash-mounted voltmeter so you can SEE what is going on with your electrical system. 1979?? it could be anything…Step one, make sure your battery post connections are corrosion-free. Remove them and clean everything up. A high resistance connection can fool your voltage regulator…

My battery is about three years old…had a load test done on it when they were testing the alternator. They did that first and determined that the battery was fine.
I know this probably sounds boneheaded but I am going to wait until it is dark and move the wires around and see if I see anything obvious. Still have no idea where to go with it.
I have a schematic (Well a Chilton book)just is getting me a little more confused.

I cleaned the battery terminals really good when I replaced the Alternator…and again when I went to the local grocery store and it failed to start. I am going to the parts store tomarrow will check into the voltmeter. Also was thinking of checking into a new fuse panel. Kinda reaching for things here.

BTW you can buy a volt meter than just plugs in the power point (lighter).

One thing I haven’t seen mentioned is the belt. If the belt is too loose the alternator won’t charge properly and if it’s too tight it can burn out the bearings. Also it’s possible the new alternator isn’t the same rating as the old one. An alternator is rated on the amps it puts out. Older cars are more likely to have several different alternators available because of all the options that are now standard. Things like A/C, power windows/locks, fog lights and even the radio all draw power from the alternator when the engine is running and were often options on older vehicles. You might need to get an alternator with a higher amperage rating than what they sold you.

A better test for the function of the alternator is an ammeter instead of a voltmeter. This will tell you if the alternator is actually charging when the truck is running.

What else do you have on when you lose power? If you have an aftermarket stereo with an amp, you could easily draw more than the alternator puts out and would therefore need a higher amp alternator to compensate.

ETA: The charging light might be part of the problem. Many vehicles use this light to trigger the alternator to charge and if it has burned out then you might need to replace it before you go any further on your diagnoses.

After I replaced the Alternator, then the voltage regulator I noticed the charging light was still on…so I went to a battery store and they tested the charging system and that is when they discovered the new voltage regulator I put on was overchrging, so they tested the old one and there was nothing wrong with it…they said my entire charging system was functioning correctly…the belt at first was loose on the alternator (making a god awful squeeling noise) I had the belt tightened…the squeeling noise stopped and the light went away.
My truck had no extras on it. No radio, no door buzzer, no dome light, no a/c, no power windows. The thing is, everything was fine for a little bit then all of a sudden the battery discharge problem.

Have them recheck the battery and check the connections at the battery terminals, as was recommended before. The battery might have tested fine but this could have pushed it over the edge. Also make sure you take the terminal clamps off the battery and clean them up well, checking to make sure the posts and clamps are in good shape and not pitted from a bad connection or corroded. 3 years is about half the life of a good brand battery and about the full life of a cheap battery. Being repeatedly discharged and even overcharged from a faulty alternator/regulator can dramatically shorten the life of your battery and cause it to need to be replaced.

OK, I think I will cover all the bases…get new battery cables with the terminals as well as a new battery, will get them today…let you know how that works out. My battery is NAPA brand, not sure if that is good or not.

I was just about to reply with the fact that you might want to try a new set of battery cables. After a while, they build up corrosion internally, and increase the amount of resistance. THey can cause all sorts of electrical issues, like the ones you are dealing with.


Bought a new battery, bought new cables replaced all fuses…same problem. Whil;e I had it running took to Schuck’s they tested the Alternator again said it was fine but said that their meter was not registering me starting the truck (no idea what that mean) then they said it was charging at 17 volts…I guess overcharging. But before I replaced the voltage regulator and they sold me one that overscharges and they determined my old one was not bad.

When these shops are checking your charging system, ARE THEY PUTTING A LOAD ON THE CHARGING SYSTEM? Are they reving the engine, and do you then see them flipping a switch, or rotating a knob on their tester? If not, then they are just doing a static test on it and this is not finding your problem.
I think your charging system is only failing when a load is being put on it, (as evidenced by what you said about driveing home at night and your truck started sputtering and the headlights were dim) Your truck is only failing when you are driveing it. Your “consumers” on the vehicle are takeing more out of your battery “while you are driveing it” than the charging system is putting back into it. AFTER you let it sit for a while (overnight etc) the battery IS RECOVERING and you are able to start it again.
This could be because of what jafo88fan said above which I COPIED AND PASTED HERE----> Also it’s possible the new alternator isn’t the same rating as the old one. An alternator is rated on the amps it puts out. Older cars are more likely to have several different alternators available because of all the options that are now standard. Things like A/C, power windows/locks, fog lights and even the radio all draw power from the alternator when the engine is running and were often options on older vehicles. You might need to get an alternator with a higher amperage rating than what they sold you

Also, the alternator might be the correct ampreage rateing, BUT it could have an internal (weak circuit in it, that changes to an open circuit) when you are loading it with all your consumers (ignition system, fuel pump, heater fan, radio, electric radiator fan, headlights, dash lights, turn signals, etc)

Post back and describe what you saw when these shops were “testing” your charging system. Describe the tester they used, and what you saw them do.
Also look on the alternator and see if you can see the amp rateing on the label and post it here. It should say something like 14v 60amp <-- avg. for that era… If it says smth. like 30amps lol

Something is not right here if they measured 17 volts at the battery. That’s almost impossible. The load meter did not register the voltage drop from the starter?? THERE IS A BAD CONNECTION HERE SOMEPLACE!! 30 year old wiring, the possibilities are endless.

Your’re right Caddy, smth ain’t right. I’m leaning towards a “loose wire” betwixt the mechanics ears, AND/OR poor test equipment. What kind of test equipment doesn’t test starter draw, and shows 17v output? What tech doesn’t test the alt. under a load to see if it’s puttin enough out when all the elec. consumers are on, not to mention that zillion dollar stereo sys, with power boosters and subwoofer :slight_smile:

OK…I had to leave my truck running because I was afraid it would not restart. He told me to turn off my truck…hooked up some wires to the battery. I started the truck (two slow revolutions from the starter and it started)it was a long box scanner thing (looked like my multimeter…Digital) he turned a knob and then said “it is not registering when you start” then told me to come out and showed me…he said “it is way overcharging…your voltage reguator is not functioning is my guess” then he showed me the meter thing…it registered 17.2 volts. He said my battery would be useless if I left it in there. He did not have me rev the engine…just start it.
Here is the info on my Alternator:
Part # 14273 Green Plug, Std Size Unit; Amps: 50
I know the voltage regulator they sold me was the wrong one, so I am now woundering if the Alternator is wrong.
Also noticed something else. I was replacing the negative battery cable and I hear a cracking noise. I looked down and there was a wire that ran from where my negativecable was attatched to the chassy over to the engine block. I took it out because it was practically bare…was this wrong?
Green Plug, Oversize Unit; Amps: 55

OK Lets cover this wire first. You may have found the problem with this truck. That wire that you just found, that is a ground wire and it needs to be on there.
If it is ragged, or burnt or not serviceable, replace it with a new one. YOU MUST HAVE THIS WIRE ON THERE, and it MUST be clean and tight where it attaches on both ends…
By saying “practically bare” do you mean it did have insulation on it at one time and now it is mostly burned off?
Was it loose on one end or the other? It must be tight. If it was loose this could be causeing electrical problems.
Same thing if it shows signs of heat or burning (this would indicate it was loose).
You need to fix this before you continue.

Also you say “your negative battery cable is attached to the chassis”?
IF this is correct, then that “other wire” (that runs from the chassis to the engine) better be the same guage (diameter) as your battery cables because it is carrying the same load as the main battery cables.
Most battery “negative cables” are connected to the engine, and then a separate ground wire serves as an engine to chassis ground connection. There should also be a body to chassis, and/or body to engine ground.

AFTER you have fixed this wire, you have 2 choices.
You can do a driveway test before you go off and maybe get stuck somewhere, or you can go to the repair shop.
If you want to check it yourself, start your truck and turn on everything, including the headlights. It’s best if you do this after dark if possible because it’s easier to see the results. If doing it in the daylight then you should look directly at the lights, not at what they are illuminating. Let it idle and look at what the headlights are shineing on and see how much it is illuminated. Now rev the engine up to about 3,000rpms. The lights should get brighter. If they don’t get brighter, then it’s time to find a repair shop with “real test equipment”.
It’s time to get on the phone. You need to find a shop that has a battery/charging system tester that incorporates a “carbon pile” load inducer so they can test if your alternator is actually putting out any amprege when there is a drain/draw put on it, ie: This replicates you have your consumers(lights etc. turned on.) They do this with a carbon pile built into the tester.
From what you described,the digital tester that was used didn’t have one, plus it apparently isn’t capable of showing starter draw.
The 55 amp rating on your alternator sounds about right for your truck considering you have very few accessories. I think they probably sold you the correct one. I think it may have been “over volting” during previous tests due to this “chassis to engine” ground wire that you found, which sounds very questionable at best.

Re: the 17 volts. The way the regulator works is this: If the regulator can’t sense that the battery is fully charged or is recieving the charge voltage/amprege that the alternator is trying to send through it, then the regulator just keeps telling it (the alternator) to “max out” and give us ALL you got…
Depending on what you tell me about the condition of this “wire” that you found, I’m beginning to think this may have been the problem all along.
I don’t know what time zone you are in but I will check back late tonight and @ 11 am pacific sat. so keep me updated on your progress.

OK, took some pictures, I hope these help, I am going to do what you said when it gets dark and will let you know what happens. I am PST gets dark at about 5-6. Oh…just got your mess. now it is 9:30 AM Saturday. Will check it tonight.

Ok, I got the pics. The old wire looks like the insulation is cracked (photo #587 & #588, but I can’t tell if it was cracked & burned due to heat or not. It definitely looks questionable and needed replaced.

What is the unplugged small black wire with the (looks like “green”) insulator boot in pic #592? ** see update below

If pic #593 is showing the battery ground wire bolted to the chassis (frame) then you are going to have to run another wire from there, over to the engine so that the engine is grounded directly to the chassis and the battery.
You can add on an extra wire for this. Must be the same size as the battery cable. It doesn’t have to be a continous wire like the original was, you just have to have a GOOD direct connection from the chassis to the engine. Make sure where you bolt it to the engine, is clean and shiny (sandpaper) and the bolt goes directly into the “engine block” not a motor mount or some other questionable attachment point that could be insulated. There should be an open threaded hole available somewhere, maybe where the orig. went to. Make sure it’s clean where the wire is touching the engine block (sand the paint off, or scrape it off)
You have to do this before you do your test or your results will be skewed

**In pic# 592 the small black wire with the green connector I’m asking about that is unplugged, is the one that the plug is hanging straight down, NOT the wire where the other green plug is horozontal.
The reason I ask is because in the upper left of the pic this black wire appears to be “melted or burned” and I was wondering if the former owner may have disconnected it if he saw it smokeing/burning.
Check it and see if it is melted/burned, and see if you can find where it might have been plugged in. DON’T plug it back in if you do find it, just try and find out where it went.

OK, sent another pic…that ground wire is burned. I looked at that green connector, I can trace it back to underneath the manifold (I think that is what that is) and it feels like it is attached directly above the oil filter…assume to the engine block. As far as the other end not sure…going to look at the schematic and maybe I can tell…I do not see any obvious plug. It was my dad’s truck before mine, I asked him he said he was unsure but he said something about a fuel pump not working and it turned out to be a corroded connection in the fuse box.
Tomorrow I am going to put that ground back on…I guess I am going to try to match the gauge…I have the old negative battery cable… would it be OK to use that? There are a couple threaded holes I can use.
I appreciate all your help, will run the test tomarrow after I wire brush all contact points.