I had a similar problem with an EQ 505R which is a 3 band pre-amp for acoustic guitar ( built it in my Squier, to make this: http://singlecoil.com/docs/active_strat.pdf). Luckily they are cheap on e-bay, but it took three that didn't work, before I finally took my DMM and discovered that the red wire was "-" and the black wire was "+"......... 
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