Electrics: Trailer Light Hookup

[mustangarcher]

Hello. I bought a wiring harness for my 2001 v70 and plugged it into the car. On the trailer, the tail lights work and the brake lights work. The turn signals do not work unless the brakes are applied. I assumed it was a problem with the adapter built into the wiring harness, so I bought a Hoppy adapter and wired it into the harness and discarded the supplied adapter. With the Hoppy, I have the exact same problem. It was suggested that I wire the brake light input for the adapter directly to the harness at the light socket. I do not know what color the wire is for the brake light at the light socket, and was also wanting input as to if this would be an appropriate fix.

Thank you,
Mike