Hi,
Checking a relay isn't difficult. Take a look at this link:
https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit
Some of the fuses do require the key to be in the run or start position.
Now, let's focus on the brake lamp issue. The brake lamp circuit is straightforward. We need power to fuse 13. Are you certain there is no power? If there isn't, then either we have a faulty fuse box or there is a wiring issue to it. Make sure the connector pins aren't pushed in further than they should be. Let me know.
Next, if you look at the pic below, it shows fuse 13. Power from that fuse goes directly to the brake lamp switch. The power supply wire is light green with a red tracer. Confirm power there.
The power out wire is light green. It should have power when the brake pedal is depressed which closes the circuit in the switch so the light will turn on. If there is power, confirm there is power out and let me know what you find.
Take care,
Joe
See pic below.
Image (Click to make bigger)
Saturday, July 8th, 2023 AT 9:05 PM