With the circumstance as you describe, you have to have two problems, for it to affect both sides. That would be what makes it confusing, I guess. Do you have a 12v test light? With a few simple checks with a test light, you can determine what you do not have at both sides. Removal of the bumper fascia should not have caused a concern, but then again, anything is possible. One thing is for certain, the fact that the high mount is working, confirms a few things. That the brake pedal sensor is triggering the EBCM to close the BAS relay and energize the circuit, so you can rule out the BPP sensor, EBCM, and BAS relay as being possibles.
With a test light I would connect one end to ground, and probe the white wire(circuit 17) at one side in the rear, and the other side, with the brake pedal applied and the key ON. This will tell you if you have a signal at the rear lamps. If you do, then check the grounds G402, and G401. Both of those grounds are in the trunk, rear of the wheel wells. Unless the specific wire for the each lamp was removed from the grounding points, to have a problem with ground is going to cause problems with many other systems. Both G401 and G402 are ground points for several systems.
If you don't have a test lamp lit at each rear lamp(on the white wire), then trace back to the next connection, which would probably be at the rear fuse block, or that joint connector. If there is power on the appropriate circuits there, you have a wiring problem between the fuse block, and the rear lamps, on both sides. If you have power and ground at the rear connectors C411, and C410, then you either have bad sockets, or bad bulbs. Let's go back to the symptom, you DO have a high mount when the pedal is depressed, you just are lacking the right and left brake light, correct? To answer your question that you asked while I was composing this reply, you only have the one relay, labeled BAS. You should be able to locate it with the legend under the fuse box cover.
Tuesday, April 23rd, 2019 AT 2:28 PM