An additional relay for the remote of the radio is normally only necessary when you connect it to an amplifier that demands more input (power) to switch on as the head unit provides...As long as the output of the radio remote matches the remote input of the amplifier you can connect to more as one amplifier without any possible problem...

greetingz,

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1990 300SL-24
1993 C250D with a minor 600+k kilometer
www.MBenzNL.com(the Netherlands)