Check your ignition switch. As stated earlier it switches to 12 volts during cranking and 9v during running - but with a bad / intermitant ignition switch you could be getting 0 volts during cranking and 9 with the key in the run position. So you need to check voltage at the distributor DURING the cranking when it is not starting - cause if it's intermitant like you say, you'll only find it when it's not working.
