This illustrates a common difference between factory and aftermarket radios, at least factory radios of our vintage. Way back in the olden days of manually-tuned radios with no clock, there was no need for a memory wire. Just a switched power source. With the introduction of electronic tuning and built-in clocks came the need for two power wires, one switched and one unswitched. So they just added an unswitched circuit that draws a teeny tiny bit of power for the memory.
A lot of newer aftermarket radios turn that on its head. That is, the main power for the radio comes via the unswitched circuit. The switched circuit is only used for power on/off triggering. Unfortunately most '90s-era vehicles are wired with BIG wiring for the switched circuit and small wiring for the unswitched, which is the exact opposite of what newer head units need. I used to be on a Saturn forum (old wagon is still sitting in the far back of the driveway), and on the old S-Series this was such a major problem that the added power draw of an aftermarket radio unswitched circuit would melt a critical connection in the interior fuse box.
