When you measure all the wires, one is constant (12v), and the other is only constant (12v) when you hit the brakes? I don't know how the EVO-R light works, but if it does the flashing internally, then something is wrong with it.
It's 12v, so you can wire up +/- to battery terminal. Based on my assumptions the 3rd wire is "switched," so momentarily connect it to the + terminal. If it doesn't flash, then the internal flashing circuit isn't working.
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