s light on my honda

1991 honda runs great most the time.when i park and shut off the car as i do an errand and when i want to start it, the s light starts flashing and my car wont start but it turns over. so i wait patiently or fiddle the ignition switch to on off, on off, till the light clears. then my car starts. has done it on a cold start too. when normal i can hear a click under the dash when i turn ignition on, engine off, before i start angine to see check engine clear after 2 sec. and "s" light clears also, then its a go.abnormal is i dont hear the click when i turn ignition on, engine off, "s" light starts flashing then the car wont start till it resets for whatever time it takes.