Ford F150 Heritage problems with lighting system.

We just purchased a used Ford F150 pickup for our nephew. The lights were all working and then all of a sudden the blinkers and brake lights quit. My husband bought a manual and it suggested changing out some little plug located under steering column on the right side. I can’t remember what they are called but it was 2 square plug ins.

Replaced these, lights worked perfect and then went out again on the way to school. Please help. What would you suggest we try?