LED's don't die... not a whole bunch of them at once anyway...
So the problem will be either no Ground, no Switched +12V or as TiTan said a dry solder joint.
make sure you have +12v going to them with the brakes on, and make sure they are getting a connection from the Ground wire to the chassis somewhere.
If you have both of these things, I'm sure they will be fixable
Cheers