BLS;
I agree with Sw&Ge...Headlights/Tailight and Brakelights are normally separate circuits, and simply connecting across the (dreaded hydraulic! See:
https://www.sw-em.com/safety_bulletin_1.htm ) Brake Light Sw (with Ign ON) should energize Brakelights, and this is a perfectly acceptable manner of checking Br Lt Sw function...if stepping on the Brk Pedal (again with Ign On) does not result in the Brk Lts being powered, the switch is in need of replacement (or upgrading to a Pedal position sensing Sw).
...BUT Brk Lts and Tailights also share a chassis connection at the Taillight fixture (see:
https://www.sw-em.com/Amazon_Rear_Li...estoration.htm ) so a poor chassis connection here CAN inadvertently connect these two circuits with strange symptoms...
Good Hunting!