The left side is the cathode (bar part of the diode symbol), the right side is the anode (arrow part of the symbol.)
Not sure how it needs to be installed, but if the installation instructions show the symbol, install the banded end of the diode where the bar part of the symbol is.
With that said, I've never had to install a diode with a Pertronix. I've always just installed the module and the interrupter and fired it up.
