Just to be clear, we are talking about the switch at the pedal? Or the relay in fuse box under the hood?

If it is the relay under the hood, replace the switch. Check the ground in the trunk, its under the interior of the trunk, near the taillight. There is a wire that is bolted to the body. If that is loose, corroded, or broken fix that. You could also check the bulbs, sockets, and tail lamps for frayed, burnt connections, etc.

If it is the switch on the pedal assemble. You might need to check all those other things as well. The switch might be blowing because too much power is going through it. A short to ground. Check the relay.

The issue with the diagnostics you will have is this is all most likely wiring issues. Something is shorting out the switch, either too much power from the source, or not enough resistance in the circuit.