Bộ kiểm tra dây tín hiệu CT-04 Cable Tester 
( Hotline : 0908815468 Mr Hùng )
Accuracy Pro Audio CT-04 Network Audio Rj45 And USB Line Cable Tester With Black Color

Using tutorials:
Step 1: install the battery. If the "betterycheck" green light is on, it means that the battery power supply is normal and the wirefinder can work normally. If it is not on, please reopen the battery box to check whether the battery polarity is reversed or whether the battery is charged.
Step 2: connect the wire and insert the wire to be tested into the corresponding jack of the wire tester.
Step 3: check the wire, turn the knob to the "1" position, and the yellow light and green light are on at the same time, indicating that the "Pin1" connection of this wire is OK. Then turn the pull knob to the "2" and "3" positions. If the LED lights are on one by one, it indicates that the "Pin2" and "PIN3" of the wire rod are connected normally. If the cross light or the light is not on, it indicates that the wire rod is welded incorrectly. Follow this procedure to test other wires.