Hi trucker, I am now 22 weeks pregnant and both the tests I used back in July came back with a faint blue line, so it sounds to me like there is a strong possbility that your wife is pregnant. It depends how much human chorionic gonadotrophin (the hormone that the test detects) is present, I obviously didn't have much at the time.
Look out for other pregnancy symptoms in your wife ie: fatigue, nausea, swollen breasts, the usual. Good luck and I hope you get the result you hope for. Keep us updated