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Trouble connecting Vcc2 to SN754410

I've tried looking around a bit and expect this to be a fairly basic question, but nonetheless I still can't get it to work. Basically I have an arduino connected to a SN754410 motor driver powering a lego motor. This all works fine until I try to use a second power supply (9V battery in this case) instead of the arduino's 5V output. Here's the current setup:

 

SN754410 Test LayoutNote that the arduino is running off of USB power.