Well, most often 1.5 Volt batteries are wired in series so the voltage is additive. 1.5X8 = 12V. I'm sure it does not draw much so amperage is not really a concern - 16 to 18 guage wire will probably do fine. Just tap in to a fused circuit like your other accesories.
BTW, I'm an AE so my answer may not count.
