Originally Posted by PPPRob

I had a V5 sti that seemed to blow number plate bulbs every month or so and I just kept replacing them.

Now I've got an 04 sti the same things happening!!! Anyone shed any light (hahaha:rolleyes: ) on why this is?

Almost every scoob I see in the dark has at least 1 bulb out :wonder:

Check for yourself!

Originally Posted by John 37

This is an unfortunate little known side effect of Subaru's decision to optimise their specification for the US LHD market and the fact that most of the vehicles development took place much closer to the equator than we are here in UK.
Subaru vehicle wiring is designed to resist the effects of other vehicles electro-magnetic influence when passing left side to left side. This is managed by loom routing within the body shell and cable bunching and arrangement within the loom. There were many problems with this during the development phase and the use of switched ground load control was an attempt to overcome these by minimising the inductor/capacitor imbalance.
The induced EMF that results when vehicles pass right side to right side is much greater and when this is combined with the Corriolis hysterysis due to the bulb filament being coiled anticlockwise, early failures are inevitable.
In higher latitudes, the earths magnetic flux is at a much more acute angle to the surface. The result is the creation of a much greater torroidal component of the phase differential within the vehicle wiring in much the same way as the Corriolis effect above. As I’m sure you all realise, this generates an ELF (extremely low frequency) reverse EMF operating (typically) in the nanoHertz range. This can cause the relevant lighting circuit to phase from normal to dormant over many days or even weeks of use. The effect is frequently assumed to be a blown bulb and as replacing the bulb seems to cure the problem, the diagnosis is taken to be correct. In fact, replacing the bulb with one containing a different coil inductor signature simply resets the ELF EMF to a null condition. However, the effect is short lived as the traxational characteristics still apply so the problem re-establishes itself in the usual time frame.
Hope this helps everyone. It’s quite simple really when the base cause is understood.