If your system was working correctly, the dashed lines would turn into small blocks and the harder you pressed on the brake peddle, more blocks would display like they were advancing from left to right, similar to a horizontal line graph but dynamic, giving you a visual display of the amount of braking pressure. If you make the tester that was described and for which you can find pictures if you search for them, (or see here https://www.youtube.com/watch?v=mhzkx7ymhJA) and attach the tester to your 7-way receptacle, you would get a 'TRAILER CONNECTED' message and when you stepped on the brakes, IF THE PRESSURE MODULE WAS WORKING CORRECTLY, then you would see the blocks advance left to right. That would tell you if your truck-side system were working correctly. If no advancing blocks, like heymccall says, try a new pressure switch. Doesn't cost much, very easy to do. According to ALLDATADIY, it is a .9 hour job a the dealer to change the switch, plus their cost for the switch.