# Battery Light on.... No.. its NOT the alternator.



## micaheli (Dec 30, 2006)

Okay.... this is a really weird problem... The battery light by itself is coming on right when I hook a fully charged battery up to the car. Even with no keys in the car... Completely off.

The light ironically stays on and drains the battery dead overnight.... Thats like water that makes you thirsty.

Anyways... The alternator is good... after the battery died the first time from the light. I jumped the car. It ran great.. charged the battery up wonderful, etc... But the damn light won't go out! 

A little history... I *WAS* having an alternator issue a couple weeks ago, but I ran new wire between all of the points in the charging system.. Some of the old wire looked really oxidized and corroded. But, that was pretty simple point A-->point B stuff... I did one wire at a time so I didn't confuse them, and double checked my work in the haynes manual (albeit not the most accurate book). 

From my understanding, the battery light goes to the ignition switch, then to the alternator... how in the hell can it be lighting up if I don't even have the keys in it?

Anyways... help is appreciated... I have to get this pile running.

--Micah


----------



## dvdswanson (Nov 6, 2005)

recheck your wiring, you got one going to something hot all the time. I know you said you checked it, but if it wasnt doing it before and now it is, do the math. you got something crossed.


----------



## Xeno (Oct 5, 2005)

Those lights work like so:

Always hot when ignition is on, then when a diode fails(in alternator) it produces a ground that lights it up.

X


----------



## micaheli (Dec 30, 2006)

So if its on when no key is inserted, I have a wire connected directly to the battery that SHOULD be connected to ignition switch.


----------



## golfer (Aug 21, 2006)

micaheli said:


> Okay.... this is a really weird problem... The battery light by itself is coming on right when I hook a fully charged battery up to the car. Even with no keys in the car... Completely off.
> 
> The light ironically stays on and drains the battery dead overnight.... Thats like water that makes you thirsty.
> 
> ...


What year & model vehicle ???


----------



## Xeno (Oct 5, 2005)

micaheli said:


> So if its on when no key is inserted, I have a wire connected directly to the battery that SHOULD be connected to ignition switch.



Well, there is also a relay that produces a ground for the light when you turn your ignition on (to test the light). That is how most of the dummy lights work (and a lot of gages).

So only a few things can light the light:

1. Bulb not isolated and is receiving ground or ground wire(to alt/reg) shorted out.
2. Bulb receiving hot other than from ignition (your case).
3. Diode fails in alternator and produces ground.(how it should work)
4. Relay failed and produces ground all the time.

But #2 only explains 1/2 your problem. (why it lights without ignition) the other half is why it lights at all? Because it should not receive ground unless the diodes are bad!

Oh and that small bulb for the alt light (battery light) should not drain your battery overnight.
Also most cars only have a few hot wires that are ALWAYS hot.
1. Battery to starter
2. Battery (or from started) to alternator. 
3. Computer memory
4. (lighter?/dome light/lights/radio memory)

So it has to be one of those that are discharging your system UNLESS there is short.
Find out by pulling the fuses and or disconnect the battery/alt.

X


----------



## golfer (Aug 21, 2006)

Xeno said:


> Well, there is also a relay that produces a ground for the light when you turn your ignition on (to test the light). That is how most of the dummy lights work (and a lot of gages).
> 
> So only a few things can light the light:
> 
> ...


There isn't necessarily a relay for the battery lamp ... depends on what model year.

Actually it's the IC regulator that completes the circuit for the lamp to come on (normally) for two conditions : no output and too much outpput from the alternator. 
But that's not the case here.

This problem is likey the wire from the " L " terminal of the alternator being tied into battery ( constant ) power which is incorrect.


----------

