I purchased a small, 2" dia, VDO Volvo Tach that fits in the center console area above the little tray for small change etc. It works, sort of. When I hook it up, Green (-) wire to negative side of coil, red (+), to battery, and black to ground, it registers rpm but the engine does not run smoothly. Also the rpms are not accurate. Checking with a proper Sun tune up kit, when rpms are 1500, the tach reads about 1000. The tach was made for Volvo because it says 'Volvo' on the face. Is it possible that this tach is for some other kind of Volvo, maybe a turbo or something or maybe one with different electronics? My 1981 is K-Jet with Bosch electronics. Its not the Chrysler set up.