Troubleshooting Vehicle and Trailer Wiring/Lighting Functions

Question:

Have a Porsche Cayenne with Pollak PK11893 7 pole outlet and pollak 7 to 4 plug. all I get is flashing lights on my test set. Can you help? thanks. Solid light on + , flashing on running lights and turn back up L/R.

asked by: Tony

Expert Reply:

The single most common cause for weird behavior from vehicle and trailer wiring/lights is a bad ground connection. A weak ground may allow normal operation for some functions but not for others. Check the main white ground wire for both the vehicle and trailer wiring harnesses; both must make solid contact to clean bare metal. Some sandpaper can help expose bare metal.

Also, note that some vehicles will not react well to certain specific wiring testers. The best way to test both your vehicle 7-way socket and your trailer wiring is to disconnect the two and test each one individually.

For the vehicle you can apply a circuit tester like # PTW2992 while a helper activates the vehicle's light functions one at a time. Please refer to the linked video showing use of a tester. Ground the tester and apply the probe to one circuit at a time. The linked article will help you identify the pin for each circuit.

On the trailer you can test easily using a set of jumper cables and two lengths of wire. Connect the cables to a well-charged battery and use the pieces of wire to connect the negative to the trailer plug's ground pin and then again test one circuit at a time with the positive lead. The linked photo shows you the pins for each circuit. If this application of direct battery power makes all light circuits function then you know to focus your troubleshooting on the vehicle.

expert reply by: Adam R