Well there is only one input for all three brake lights and that is the switch. However, as the top light is out the problem is probably not the TIPM as the CHMSL light (top one) does not run through it other than the fuse. Also, the turn signals also run through the TIPM on the same wires so it seems you only need to find the problem in the brake switch circuit.
For testing you only need a simple test light and a piece of wire. With the test light connected to ground touch both of the tabs on top of fuse 26. That fuse should have power all the time. If the light comes on with both tabs you can then move to the brake light switch. There you can unplug the wiring connector and check the contact on pin 1 (gray wire/red stripe) for power. If you have power there the next step is to be sure the switch is working. Plug it back in and find the white/tan stripe wire. This is the brake output wire. Use the test light (you can strip off a tiny sliver of insulation and probe it then apply some liquid electrical tape to seal it again). With the brake down so the switch is on there should be battery voltage on that wire. If you find nothing it is probably a broken wire in the connector or in the wire itself. The way the system works that wire is a direct feed to the CHMSL light and tells the TIPM that you are on the brakes. It goes to a splice and splits there to go to those items. I believe that between that splice and the switch is where the problem is. The voltage is not getting to the splice or the splice itself has failed and you lose the brake lights.
A way to verify that is the case would be to remove the CHMSL lens like you were changing the bulb. The bulb just pulls out, there are two connections, one goes directly to ground on a black/tan stripe wire, the other is the white/tan stripe brake feed from the switch. If you use a jumper wire and feed battery voltage to the white/tan stripe wire with the key on you should see the other brake lights come on as that simulates the power from the switch.
Saturday, February 27th, 2021 AT 1:46 PM