This tester has one side to connect the 7-pins plug of a trailer and another side to connect the 7-pins socket of a car. This tester indicates quickly if a failure concerns the wiring of the car or the wiring of the trailer. Features: Can effectively test what the problem is for 7 pins plug and socket connection. Carefully selected materials, frosted surface. Cross slotted Copper needles, cooperate with the female pin. The cross slotted of size is easier to control. (The size of the a slotted is not stable) Safe and dependable performance, reasonable design. Deft appearance, convenient usage. Specifications: Main Material: ABS & Copper Color: black Item Type: Diagnostic Tools Item Name: Trailer Tester Size: approx. 20 * 5 * 4cm Battery Type: 9V (not included, you need additional purchase) Package Size: 20 * 5.5 * 4.5cm / 7.9 * 2.2 * 1.8in Package Weight: 194g / 6.8oz Package list: 1 * 7-Pin Trailer Tester Tool Function & guide: Trailer (can also be a caravan or bicycle carrier) Ⅰ. Put the plug in the connection of the tester. Ⅱ. Press the yellow button on the side of the tester. Ⅲ. If the wiring is good, all the LEDs light up. the function of each LED is (acc lso 1724): ⒈ left hand indicator (yellow); 2. foglight or 12V (blue); 3. mass (white); 4. right hand indicator (green); 5. right rearlight (brown); 6. left brake light (red); 7. left rearlight (black). Attention: The pin no 2 can be used either for a warning foglamp or a permanent 12V connection. Ⅳ. If a LED doesn't light up, it is because the corresponding wire is defective. If all the LEDs don't light up, then the mass wire is damaged or all bulbs are defective. Car, camper 1. Put the tester in the socket of the car. 2. Press the yellow button on the side of the tester. 3. If the wiring is good, all the LEDs light up. Do again steps 4 as previous. You can also test the functions of each pin of the socket. 1. Switch on the left hand indicator (after switching on the ignation key). 2. The corresponding LED must flash with the same frequency. If not, left hand indicator wiring is defective/broken. 3. Repeat steps 1 and 2 for the right hand indicator, rearlight, foglight and stoplights. With a +/- 4 m extension cable, you can test the functions form the driver's seat more easily.