What have I done!

[Robin Hewitt]

I usually get completely the wrong end of the stick but let's have a go.

If you fitted a relay and everything went wrong even after that relay was removed...

This would suggest the relay had no protection diode and what ever you were using to drive the relay also drove the thing that no longer works.

You probably know about protection diodes but just in case. Current flows through the relay coil. A semiconductor device attempts to break the electrical circuit. The coil inductance requires that the current continues to flow, the volts go through the roof, the break down voltage of the semiconductor is exceeded and the magic smoke escapes. A protection diode across the relay coil allows the current to flow back through the coil until it dissipates.