Electrical gremlin.....HELP!!!

[Plums]

Houston, I have a problem!

The battery light in the Ute is on and won't go away...

Yesterday I was under the Ute (VY SS) checking out the alternator/starter wiring so I can wire up the Cobra. I was pulling back a small bit of insulation tape (with pliers) when I inadvertently shorted the brown wire to the chassis. This shortout was very brief - almost not noticable - and I didn't really pay it any attention. That is until I started the car!!! As soon as I started it the "Check Alternator" warning flashed up on the display and the battery light stayed on

Here is what I know:

1. The brown wire goes to the dash for the battery light.

2. The battery is definitely charging because there is 14.5 Volts at the battery when the engine is running. (The normal range for this particular Alternator is 14.1 V to 14.7)

3. I have checked the fuse that is supposed to be for this purpose (F13 under the dash) and it's ok.

Have I blown a Diode that will now let the battery discharge? Have I blown up the alternator (even though it's still charging)?

Can anyone help me???

Cheers,

Plums

[Gav]

I would think that a diode would be a little more robust than that your suspicion is probably the case.
I found that my alternator had enough residual magnetism to re-exite itself on start up without even having an alt lamp in circuit.
I'm not sure if thats good design or not!!

Gav

[hogster]

My Pajero suffered a similar issue a while back, my brother in law (auto sparky) told me to disconnect the battery completely and let the car sit for a few hours, if you haven't already tried.

Apparently there is some sort of fault memory in the engine management system, and left for a few hours without power it just cleared the fault by itself. Been fine ever since.

I don't understand stuff I can't see.

Hogster

[Plums]

I drove the Ute across town today (1 hour drive each way) and watched the battery voltage (in the diagnostic display) very closely. The voltage hovered around 14 volts all the time, only dipping down to 13.7 when the thermo fans came on at traffic lights. The alternator is therefore charging correctly....

I will certainly try disconnecting the battery when I get home...

[sideshow]

unplug the alternator plug wth white and the brown wires on it

then start the car does the light still come on

if it goes out then u might have sorted out something in alternator

if the light still comes on the might have a short in wiring

or problem in dash but the brown wire should not matter if shorted to ground

so it should not spark

so i guess u might have shorted the brown to the red wire which is battery power

so u prob fried the alt

but if u unplug the plug off alt and light goes out then u have prob in alternator most prob

thats y auto elects charge alot heheheeh

so incase they do stupi dthings like that

[Aussie Mike]

Hi Bobby,

If you think about how the charge light works it should be fairly easy to work out where the problem is. The charge light has +12V battery on one side of it and the brown wire from the alternator on the other side. When the alternator isn't charging the brown wire has a potential close to - ground so current flows from the 12v on one side of the bulb to the ground potential and lights the bulb. As the alternator turns and starts charging the potential of the brown wire increases bringing it closer to the +12V battery. Once it's voltage reaches the same potential as the +12V battery no current will flow from the +12V on one side of the bulb to the brown wires now +12V potential and so the bulb goes out.

If you disconnect the alternator brown wire the dash light should go out as that's where it's supposed to be getting its ground from. If it doesn't then you may have a short to ground back in your loom somewhere.

I believe the white wire is the exciter. This will be connected to ignition battery and will fire up the field winding when you turn the key so the whole thing starts charging.

Cheers

[sideshow]

white wire is the sense wire and is battery not ign

so i usually just loop the white wire from the big battery terminal on back

of alternator to the whte wire plug

then just run the brown thru engine harness up to dash

[Aussie Mike]

Sideshow, you might be able to clarify this for me. Will the alternator produce a charge if the white wire is disconnected?

I always thought is was a way to shut down the alternator output when you turn the ignition off. Otherwise you could get into a stuation where if there was a wiring fault somewhere that the engine could keep running if the battery was disconnected because the alternator had enough output to excite itself.

Cheers

[sideshow]

new cars these days can run into that rpoblem if relays are wired up wrong

anyone fitted yr normal redbattery cut of switch can have these probs

so the proper red keys also have small terminals on ther eto cut coil power

u will see coil power runs thru ignition not thru a relay on most toyotas

so when key is off power is lost on coils andengine stops so alternator stops charging

alt will only charge when spinning anyway so as long as yr relays are wired ok u should be fine

wiring faults usually dont cause engine to keep runnin on a std vehicle

they just make it run bad