Radio loses presets.

[Jesda]

I've tried two factory radios and both lose the presets if I take the key out for long enough. I also can't get my Alpine head unit to turn on. Could it be a bad 12v constant? Where do I start diagnosing something like that?

1993 S13 convertible

[qsiguy]

Just get your test light or multimeter and make sure you have 12V+ on the constant wire when the key is off and on. We can assume your switched power is working if the radio is coming on when you turn on the key.

On most Nissan vehicles the OEM constant 12V+ wire is Red w/black stripe and the switched accessory wire is blue.