motor wont start, where shud I start?

the 360 I built last year has been starting and running like a champ, until just a few days ago... Now it wont start, intermittently, until it decides it wants to. It turns over and over but sounds like not getting any spark.

Note: it seems if I turn the key off then back on a couple times it suddenly gets juiced and fires right up. The ignition switch in my 71 demon died long time ago and I rigged up a toggle/rocker switch to actually start my car after I turn the key to ON position.

My motor is mostly stock with a few upgrades... cam, carb and intake. I put electronic ignition on it when I rebuilt it last year and it has the famous "orange box"

I dont know where to start troubleshooting this. Can someone tell me the first few things I should check? Thanks!