Do a google search for Thunderheart. They have all the wiring diagrams on their web site and there is a trouble shooting section in the manuals also.
Have you checked the simple things like power to and from the key switch? Have you checked for spark at the plugs? Look for simple things first. It could be a broken wire or sometimes when a new battery is installed a ground wire slips away and does not get reconnected.
Good luck! Post some pics of you're bike when you can.