"SC" wrote in message
...
Thanks for the advice. Is there any particular reason why you would use a
relay rather than wire it straight into the ignition live?

A relay will draw a minimal amount of current from the ignition circuit,
they are cheap enough and only 4 wires to connect, 12V switched from the
ignition, 12V from the battery , a feed to the head unit and chassis.
And is independant of brand on modern cars.