Hi! im new around these parts so to start i just wanna say HI

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I recently bought a 94 csi seca 101R and it has no tacho! bit sad but i went out and bought an aftermarket Speco 2 5/8" tachometer here is my problem. *I couldnt find an answer on these forums for my problem* The Green wire which is meant to be attached to the neagtive lead of the coil I just dont get. Is there a wire already in the dash I can tap into? I read somewhere its black which doesnt help much. Instead could I hook up to the test bit on the side of the engine bay without going onto the actual coil inside the dizzy??
please help! am tacholess!... not good!
thankyou everybodies