I have the sds with a dis-2 installed on a 90 miata using the factory tachometer. My tach is jumpy everywhere except idle and medium throttle. should i put a tach adapter on my car or does anyone else have any suggestions.
Thanks in advance.

First before spending the money.Id go over everything with a fine toothed comb.As it is possable, that a wire is affecting it and perhaps at both ends due to that could be the ouuter limits so to speak in not enoug for its needs or to much to get it all to the point.So Ive even seen many times where a wire will be broken from not being secured properly and its weight and vibrations move the wire finding it weakest place and there is where the break will happen as its flexed back and forth untill its a gonner! And not always easy to find unless ohmed out and even then if the wire if pushed back it will read fine and the same in the connectors used and how there crimped into place.AS they should alway be done from the back of the split as thats the front lest say.IF you crimp from the split face they almost never will crimp as they simply more often than not come off almost as fast as youd put it on the wrong way.IF in doubt always solider them on! Thats the best and if you have a conector as in male and female.And most havent any covering for shorting out? I always cut some shrink tube and slide it into place covering then and shrink it! As for your grounds? You should one use not stainless but a metal screw which any magnet can lift.Then use sand paper and clean all rust and paint away to get the very best in all grounds as they are alot more important than most give attention to!Then your keyed power wire should be fusedif you dont want a fryed tach? OR worse.And as for the green usually wire.Id connect it to the unit rather than the coil when ever possable.And if not then thats all you can do.But it seems to be alot harder on tachs?Maybe alittle to much Id think.And if none of this works then yes get the adopter.As for myself and as of right this moment! Ive never had anything but a fryed crisp tach no matter what the hell the instructions have said? Im going to send this autometer super comp back and have it repaired as I try a summit racing and cheap unit for the time untill?And if these two go then Im done period as whats the point other than to drive a tack up ones rear! As Id tryed them on my harleys and all in the same rotten results! Only the factory tach has at all worked and at that only in my 85 toyota and fourwheeled alot no less? Go figure?