1 faulty brake light switch, 2 faulty wiring from switch to taillights. Possible short on trailer jack (if fitted).
Are both your brake lights blowing out? If it affects only one light: it could be a bad light socket, or a pinched or frayed wire that is shorting out.
It's because you have a short current somewhere. You need to check the brake light wiring.
short in electrical circuit
1. a bad ground wire, or 2. a short in the brake electrical system let me know if it helps?
Are you blowing fuses or are the bulbs blowing? Blowing fuses would be a sign of any wires or metal contacts in your brake circuit grounding out or shorting on themselves. You'll have to check all of the wiring in your brake light/switch circuit to be sure.
It is possible that one of the bulbs is shorting out. Try replacing the brake light bulbs, if that doesn't work, troubleshoot the brake light switch.
Most likely one or both brake light lamp sockets are corroded. This will short the circuit and blow the fuse. The only other most likely cause is a loose wire connection at the socket or fuse holder.
It sounds like you have a short somewhere.
SWITCH
It can if it is a dual filament bulb as found on most US. makes. The brake light filament can short over to the tail light filament inside the bulb and when the brakes light is activated, all the tail lights and front marker lights will light also, probably blowing fuses.
short circuit on trailer light wiring
Most likely your pilot light is out