I soldered directly onto the center leads. You may want to find another way to do it, or not. This works and doesn't damage anything for future use, unless you're a crappy solderer and overheat it and melt the plastic. So. WARNING: excessive heat while soldering at these points will melt the plastic, possibly damaging the unit beyond repair. While keeping the warning above in mind, make sure you don't do a "cold solder joint" that could just crack off at the first sign of a washboard road.