When installing multiple amps and using a relay to switch them on, is it ok to use the car battery directly, as the +12V source or do I have to find a regulated source? Will it fry the amps if the remote turn on terminals receive more than 12V?
Yes, running the power from bat is fine for a relay. Thats the right way to do it. And no, your bat should only be putting out 12-14 volts. It would be the same as jumping the amps rem/power terminals.