"Wring" the switch with an ohm meter. Put one lead on the "batt" terminal. Turn key to left, you should have continuity to "Acc" only. Turn key to right and you should have continuity to "acc" and "ign". Hold key in start position and you should have continuity to "ign" and "start". If not it's the switch. Sounds more like it's wired wrong though.
