Hi, hope someone can shed some light on an issue that i've come across today, car is a 1998 V4 WRX STI -

Decided to swap out the tiny bulbs in the instrument cluster for LED's to freshen up the look - everything went well, just had the cluster in and out a few times swapping the LED's around to get the polarity right so they would actually illuminate lol

Pro's - Clock is nice and bright but doesn't dim when you turn lights on
- check engine light now works - i wasn't aware the bulb was away in it
- Red warning illuminations now looks kinda pink due to brighter LED's so is more STI-ish lol
- Indicators are now very crisp on and off

Con's - now here's my issue - the battery light now stays illuminated, lights up when ignition is switched on but only dims a little once engine starts and stays illuminated when engine is running. This didn't happen when there was a filament bulb in place - can anyone shed any light (see what i did there?) as to why this happens or should i just switch it back to a filament bulb and admit defeat?

 

I'd be inclined to put a filament bulb back in. On that one at least.

Your alternator will not produce charge unless that bulb lights and goes out when starting. Indeed, the use of an LED may mean the alternator is no longer "seeing" the need for charge, and the result will be a flat battery, and another...and so on.

Keep in mind that an LED will produce no light until it reaches a threshold voltage, then lights up full power. A bulb allows small amounts of current from the off, the amount of current flowing will depend on the voltage applied across it, and so the light output will vary too. LED tends to be on, or off. That's the nature of a diode, it either passes current...or it doesn't.

 

Thanks, was fearing that it wouldn't be charging when lit up - i'll swap it out when i get home from work in the morning then go a little drive to put some juice back in the battery

 

ive seen this before with other cars and leds, i think you have to put a resister in the circuit somewere, probs after the builb that is staying on or before, cant remember

 

Usually you put the resistor in parallel with the LED so that the circuit sees it as a bulb rather than an LED - normally thats for indicators though so you don't get a rapid flash like a bulb has went.
I swapped out the LED and went back to the normal bulb - everything back to normal!

Did get a little inspired and took out the fan / heater controls and modified the filament bulb back lights in those to LED's also - i had spares from doing the instrument cluster so thought i'd give it a go

 

LOL, the modding bug bites.