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Why does the charging light go out so soon?

I drive my pickup (87 Toyota 4-cylinder carbureted 5-speed Xtracab Deluxe Longbed pickle, onions, salsa) occasionally. When it’s sat for a week or more it takes a few tens of seconds to start. I bought a booster battery to help. The charging light comes on, but it goes out as soon as the engine starts. I’m used to hard-to-start cars charging for a while after a long start. The voltage coming out of the alternator is okay. The battery is new; the density of the electrolyte is right.

You cannot really be asking such a question seriously.
Post back when the light DOESN’T go out. :stuck_out_tongue_winking_eye:

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The charging (system) light indicates that there is a failure if it stays on.

I looked at the owner’s manual. It tells me that it is a ‘discharge warning light’, that it indicates a problem if it comes on while driving, just as you 2 say. (It says ‘charge’.) This is the exact opposite of ‘charge’.

Has it always been this way? Have I misremembered those times when I noticed that it stayed on (in other, older, cars) for a while and I thought it was telling me that the battery was charging?

The “charge” light indicates that the alternator is trying unsuccessfully to “charge” the battery. The reason then needs to be diagnosed. The battery may be too dead to take a charge, the alternator may be bad, a connection may be corroded or otherwise failed, or if you have a vehicle with an old fashioned fanbelt the belt may be broken. Or there could be some other problem.

If the “charge” light goes out immediately after starting the engine, it indicates that the battery has successfully taken the charge necessary to replace the energy you used to start the vehicle.

I can’t believe I am writing this. Random Troll ( might be a correct name ) put the owners manual down and step back.

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Hmmm. Its just a switch that turns the charge light on or off depending on the voltage being sensed. As soon as you start the car, the voltage should go up to 13+ volts and turns the light off. It happens as soon as the alternator starts turning. If you had a meter instead, you’d see a slightly higher voltage after a start for a little bit while it is recharging the battery but not much.

Get rid of the salsa

Not quite Bing. If the voltage being generated by the alternator is never matched by the battery, the charge light will stay on. The battery must be able to charge to equal the alternator output in order for the light to go off.

Think of it this way: the car runs off the battery, the alternator simply keeps the battery charged. If the alternator cannot do so, the imbalance in the circuit triggers the warning light.

hmmm, not quite mountainbik. The alternator can careless how many volts it supplies to the battery and what voltage/amps the battery can hold. If the alternator overcharges it blows the warning light first. Does not happen very often because of alternator inside safeties.

When you turn your key to the on position 12V, from the battery, are supplied to the alternator through the warning light circuit. When you turn the key to start and the engine starts that circuit is reversed by a diode inside the alternator and feeds voltage back to the warning light. The warning light circuit receives ~12V from both ends and will not light unless one circuit is low or has no voltage at all.

edited to add: for $3-4 the manufacturer could add a second warning light and then it could easily be determined what is at fault, the battery or alternator.

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Thanks for the URI kurtwm2010. Neither the Haynes nor the Chilton’s have this in the schematic.

I don’t have a problem, just a misunderstanding. I thought the ‘charge’ light was telling me that the battery was charging (that it was in the connection from the alternator to the battery), that it went out almost immediately when the engine started cranking usually just meant that starting used so little energy the charging happened quickly. I have a strong memory of difficult starting followed by the charge light staying on for a while (seconds, maybe a minute) because it took longer to replace the energy used in other cars, more than 30 years ago. Was it never this way?

I do not really recall that and I have been around cars for over 40 years. I do recall that at times my charging light would slowly come on when idling at a red light or stop sign and turn off again when driving at regular speeds. We would simply press on the gas pedal to raise the rpm an all was good. Maybe, if bored, we would take a look at the belts and make sure they are tight. I don’t necessarily believe that it was a fault of the charging system, but it was a limitation of the then technology. You hardly see this in today’s car, the light is either on or off and if it is “on” one better pay attention right away before something goes haywire.

Today’s cars have a ton of electronic technology built in that requires an exact amount of current/amps. Many of those components blow their socks off with only the slides variation in voltage (mostly high spikes). Fuses have become fast-acting fuses to minimize damage to electronics, capacitors, resisters and diodes have become common in all electronic/electric components.

I would have thought that Chilton’s or Haynes have a schematic that shows the electric charging system. I guess not.

It’s kind of like the light that’s shaped like a gas pump. When it comes on, it does not indicate that your tank is being filled. :wink:


I was coming to the same conclusion that the older vehicles being referenced were equipped with generators. You reminded me of the light flickering or coming on steady at idle. My parent’s 1967 Chevrolet was the first car I drove with an alternator. Apparently someone at GM didn’t get the memo as the dash light was still marked “GEN”!

LOL, sarge, you bring back old memories.
Yup, cars long ago had generators… and the rectifiers were separate and typically mounted on the firewall. Long ago manufacturers started incorporating the rectifiers into the generator assembly and calling the assembly an alternator. :stuck_out_tongue_winking_eye:

Gen was used in some pretty late model cars until they adopted the international battery symbol instead. I’m not qualified to say why but seems to me that technically, gen was still a correct term even though it had an alternator. It was still a generator. Kind of like motor and engine I 'spose.

Are you referring to the old generators with commutators?

No rectifiers were needed on generators or on the firewalls behind them.

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Agree with @Rod_Knox. A pre sixties generator simply generated D.C. There was no need for rectifiers (diodes). The device on the firewall was the voltage regulator which simply consisted some mechanical relays. I remember you could pop the cover and adjust the charge rate by simply adjusting a screw or two. I also remember the rear bearing in the generator was simply a sleeve bearing - not a ball bearing. I used to pop the rear cover now and then to put a little dab of grease on the bearing.

An alternator is simply an A.C. generator that uses diodes to convert the output to D.C. etc etc…

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I’m sure there are still a lot of people who call it a generator. And it really isn’t incorrect. It does, in fact, generate electricity. DC rather than AC (which would go to a rectifier), but so what? Anything that generates electricity, AC or DC, could, IMHO, legitimately be called a generator.

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