Dixco tach hookup

So I got this tach off of CL yesterday and can not find any install info on it. I realize green goes neg coil , red is 12v, and black is ground but where is the light wire? I swear years ago a buddy had a Mopar Performance tach identical to this and it had a light! Can anyone give me any info on this tach and the proper wiring hook up as I do not want to wire it wrong and cook it? Thanks in advance! A few pics..

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