Paul,

At a mininum I would think that you would want at least a battery contactor to interrupt the power to the injectors, but the system will work even without that.

Tracy's system is wired in a similar manner.  The EC2 provides the ground while the other side of the injector is 'hot.'  Tracy recommends that this 'hot' wire be part of the ignition buss, but there is no reason it shouldn't work connected straight to the main buss.

Hope that helps.

Dave Leonard