Tail lights turn off with headlights on but, turn on with DRL.

[Dawson]

This has been an absolute nightmare trying to fix. I have a 2007 subaru Legacy sedan 2.5i non turbo. originally it was just both tail lights were burnt out so i replaced those to see they still didnt work. I checked all of the tail fuses with no luck. under the dash and under the hood as well. Figured that i could switch the relays for R Def. and tail relay which worked somewhat, thought they both mightve been weak, so i went tothe dealership and purchased a new tail relay. Plugged it in right out in the lot. Now title. The tail lights and license plate lights are only on with the DRL and off when headlights are turned on, counterintuitive since its illegal to drive at night without taillights or headlights. I went into the dealership and they said they could stick a tech in my car but refused due to the nature of them overcharging me for something i had a warranty for the last time. the only thing they said was that it might just be the actual headlight switch being broken. Im so clueless and cant wrap my head around how to fix it, any help is appreciated.