You need to remove the rear left panel to access the rear electronic module. There are relays back there. Replace swap relay RMI5 with one of the other relays and have some one step on the brake pedal. If lights com on then the relay needs to be replaced. If no lights come on then swap one of the shunts. They arethe flat looking ship. Swap RSH6 with another shunt and step on brakes. If they come on then replace the shunt. If they dont then you will need to take it in to a shop for further fault tracing. 99% of the time it is the relay that goes bad. The 1% would be the rear module going bad. Good luck and hope it is just the relay that is bad.