What's the easy way to tell what wire is the + to wire in aftermarket speakers

Talking in general not just rover

 

use your cordless drill battery and make a set of test leads tape one to the + side and one to - side of your drill battery. Alligator clips on other end. Attach clip to one side of speaker lead and the other lead just touch it momentarily. if the woofer cone goes up, then what ever lead you have + dc volts to is your positive lead. if woofer cone goes down the leads need to be reversed, and repeat test.( I attended a mobile electronics school and this is how they taught us). Remember, you speakers are receiving an a/c voltage (hence up and down movement of cones) the d/c voltage is one way only and not alternating. UP or DOWN. also your not gonna blow the speaker up if it is just momentary touching the tabs on speaker. (if your deck is providing 15 watts per channel, thats about 22 volts for reference). The smaller the drill battery the safer in my opinion. I use a 9volt battery. good luck

 

I came to say exactly what was said above. I simply use a 9v battery and some spare speaker wire. Watch if it pops out or in. Best of luck.