If you’ve read why there is a flashing red fault code on your Tow-Pro Elite, you should now be ready to test the earth wire connections.
Testing should be done with the trailer wiring plug plugged into the vehicle’s trailer lighting socket but with the trailer not coupled to the vehicle.
Switch on all circuits of trailer lighting and ensure that any trailer battery is being charged via its Anderson plug.
If the Tow-Pro™ LED is flashing red, unplug the battery charging Anderson plug. If the LED stops flashing red, check for a poor connection or undersized earth wire from trailer battery negative via Anderson plug to vehicle chassis. If it is still flashing red, measure the voltage drop from trailer earth to the point where the vehicle trailer socket (Pin3) is earthed to the vehicle, then from earth point to start battery earth. If a total of more than 0.4V is found, take the below steps to reduce the total voltage drop as much as practicable.