Originally Posted by wbain5280

There is an interlock. First, check the battery voltage, then check it when you start the car. You will need a helper to do this. The battery terminals may need cleaning and there is a small tool for this called a battery post cleaner.

This article will help:

http://www.peachparts.com/Wikka/W108NeutralSafetySwitch

and either clean it or replace it. Call Phil at the 'Buy Parts' section at the top of the page.