I know this is dumb but could a bad main relay cause my car to have a drain in the brake light/ horn circut?

 

i dont see how that would be possible, so i'd vote no.

 

No. The main relay only connects to the ECU and the fuel pump.

 

off topice sorta but i just found out that my bettery has been draining for the past 2 months because the rear-deforester relay was blown and thus causing it to be on all the time. ... it cost me $170 for the dealership to track down the power drainage and replace the relay.....