Quote:
Originally Posted by DanEC
Patrick - is this right? I'm pretty sure mine have two filiments - at least the fronts do I'm certain - I think the rear are the same. Or is this a different bulb the early car used?
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The tail lights, "parking lights" or "running lights," as some call them, that are on all the time for night driving, use one of the two filaments. The turn signals and brake lights use the second filament. That's the whole purpose behind the trailer relay. If the turn signals and brake lights used different filaments, then you wouldn't need the trailer relay to "marshall" the current when you had both your foot on the brake and were signalling a turn. Look at the schematic and you can see that each bulb only has one output coming from the trailer relay. That one output has to control both turn signalling and brake signalling.
The front lights also have two filaments, but since there are no "front brake lights," it doesn't matter and, thus, needs no relay to sort it all out.