I want to install a Siriusxm radio receiver in an antique car with a 6 volt system. The Sirius receiver power adaptor states that the output is 5 volts. If I wire the receiver directly into the 6 volt system, I am told that the extra volt will burn out the receiver over time. How can I reduce the voltage from 6 to 5 volts? Could someone advise me on how specifically to do this? Any recommendations on what I should buy, to include source if known, would be appreciated.