Check the battery ground.

 

I'd check grounds, as stated previously, and condition of the battery. Then, if those are good, I would disassemble the ignition switch on the console. You can test it by turning the switch on and off a few times to see if it makes good contact 'intermittently'.

Mine comes apart by removing the snap ring, then pulling the contacts out. Inside there are three springs with contact plates that complete the connection to the batt/acc or ign/batt/acc. The third contact plate is opposite side of contacts to provide support.

My switch just had a problem similar to what you are experiencing, and after cleaning the contacts it seems to be working just fine. One of the contacts under the spring was a little worn, so I simply switched it with the opposite contact which provids support. That one had no wear on it, so makes better contact now.

If that turns out to not be the problem, then I would proceed with the other suggestions. JMHO