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The reason all the LED's flicker is because Subaru uses a PWM, pulse wave modulation, for the daytime running lights. Halogens react to this by appearing dimmer, but LED's will see full voltage pulsing on and off very fast. Nothing you can really do to change that.
I went down this rabbit hole trying to have off road lights automatically turn on, via a relay, with the high beams and not the DRL's. I was able to mostly achieve that by using a second relay tied into the parking lights circuit.
 

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I wonder if a pi filter ( 2 capacitors and an inductor) would smooth out the 6 volts. That would be for the EEs to ponder.
Oh, there is no doubt that you can create am electronics circuit to filter it out. It was just too much of a pain for me to worry about. I did try using a relay thats latching voltage was less than 6v, but it still picked up the PWM signal.
What I wanted was to be able to have my A-pillar mounted offroad lights turn on and off with the highbeams. I hated fumbling in my forester to turn them off seperately when I came upon another driver. So I just made a simple logic circuit; If the parking lights are on (relay one), then the highbeams signal can then pass through to relay two, which is controlled by the highbeam signal, to turn on/off the offroad lights.
The only issue would be if you wanted to have just the parking lights on, but no headlights, then the DRL signal still gets to the offroad lights and they'll flicker. Not really an issue since I have a OEM switch that acts as a bypass, it has to be on to even allow the offroad lights to work. So it never happens in reality. Obviously the offroad lights are LED's.
 

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I was not considering off-road lights. If there's a fuse for the high beams, either in the engine compartment or interior fuse box, use a fuse tap and relay to turn on the off-road lights.
lol, um... yeah. Since the DRL's and the high beams share the same 12v source (and fuse), that isn't an option. I have a good workaround for my situation, it's people like OP that want to replace the halogen bulbs with a LED lamp that can't get around the PWM making them flicker and/or incorrectly see full power.
 
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