Your radio operates on 6 volts DC. The red wire is positive and black negative. You should be able to find a schematic here on nostalgiaair. First click on Rider by Original Index, then Zenith and model number.
Norm
: I have Zenith 4B313 Farm radio. How do I find out the correct voltage? It has two wires out the back, one is black the other is yellowish tan with red stipe.
: : Many Thanks, Jim Moore