For instance, Fords like the Focus use the accesory line which will drop to zero while the key is in the crank position and it will come up again when the key springs back to RUN/IGN. There is no ignition sense at the radio connector.

Yeah, that's exactly what I meant in an earlier post. One could test if their car was doing this thing by simply looking at the ignition sense wire with a multimeter and fiddling with the key.

Question. Let's suppose my car works this way. Let's say I want the ignition sense wire to have a slight capacitance delay so that a voltage loss didn't make it go "low" for, say, a second or two.

Can I do that with a relatively small capacitor? Perhaps small enough to be done internal to the empeg itself? How would it be wired?