I can't see anything obvious in Haynes or Porter, but if the only wiring needed is for backlighting when the lights are on, use the yellow/black for the +12, and black for earth.
(those cables are under the instruments for the clock, cigar lighter, ideogram, and switches.)
Yes...the inclinometer is a mechanical device and only needs wiring for the light.
But, purely as a matter of interest, why would you want to fit one to a standard road car ?