show us the wires, so we can make a poorly educated guess. it doesn't match the pictures in any of my Sears, Wards, or JC Wx catalogs.
I agree with tomcat11. I think it is a RAC. I bought one at K-Mart in the 70's. It is hanging on the shop wall. I will look for the instructions on Thursday when I am home.
There was a thread a long time ago asking that same question. You can view it here: Wiring a RAC GT Tach | The H.A.M.B.
Got curious and Googled it. This might give you some clues: https://corvaircenter.com/forum/viewtopic.php?t=682722 Russ
Red ... 12v + Black ... Ground Green ... Neg Coil [signal] Yellow ... Internal Coil Magneto tachometer signal Blue ... Often used for recording in playback tachometers [sometimes lights] Just hook up Red, Black, Green and try it [the worst that could happen is a "death ray" from the sky] These 3 colours are universal aftermarket colours for all rev counting devices [shift lights, tachs etc]
57 Fargo Here is a picture of my RAC tach, it hangs on the wall in my shop. That tach has been past 6,000 rpm on the infamous Woodward Ave, Telegraph Road, Haggerty Road & Milan Dragway and many stop lights. (only 6,000 rpm because it was in a GTO and 6,000 was about it for a 389) Attached are the instructions that came with the tach. If you can't read this, send me a pm with your address and I will mail you a readable photo copy. Greg
Kind of reminds me of this particular floor mounted tach in my friends Buick Wildcat, but I know that its not the same one as posted by the OP.