hmm, idk, but i found out autozone does the free code check, at least where i live... Idk if the code will tell you exactly whats wrong, but might be worth a shot... i'm not completely pisitive on the style on the wiring of the tach, etc. but on my camaro ('78) the copper bands on the back of the component could be shorted/and or burned or corroded. That happend on that thing. hope i offered some help...
-Shawn