Two loss wires to solder on stereo wireless hp's, both red, which one goes where using multimeter?

I have two disconnected red wires on the left side cups that need reconnecting to the L- & 3V on the board which you can see on the image below.

My question as a multi-meter novice, how do a test to know which red wire goes to which point?

Also is there any danger of overheating the board on so small solder points?

Any help much appreciated