Car turns over but won't start--found loose wire

Yesterday the car wouldn't start in the morning, but started up fine in the afternoon. Then this morning it started, but when my husband stalled it out accidentally, it would not start again. The engine turns over, but won't start. I opened the hood and found a loose wire (see picture) and i'm wondering a) if that's the culprit and b) where it should get plugged back in. I should mention that this is a Euro spec vehicle. Thanks for any suggestions.