Now here's a somewhat ricey question...

How do you safely get lights to flash to music?
I've been told to just hook them to an amp, but I've also been told this is bad for a number of reasons.

There is a guide to do it somewhere. Simple as a transistor, diode and pcb mic

You don't need the Mic, it can be hook of the head deck output. Also I think there are easy circuit online. Tonight I can post some up if you like.

I've been told to just hook them to an amp, but I've also been told this is bad for a number of reasons.

Depends on what your powering?

Depending on the amp, the output voltage can exceed 20-30 volts peak - sometimes more, and also dependant on how tolerant your amp is to impendence. Tacking on extra devices to the outputs will effectively lowers total impedence that the amp sees.

if it's like a handful of leds, wouldnt effect it too much, but you'd need to consider the output voltage.