No, you mistated it, and you are wrong as to the application of the Fifth Amendment.
It applies to self-incrimination, and does not apply to matters where criminal admissions are not an issue.
If you do not want to say something after an accident, it is in your example because the person knew they were involved in a criminal activity. the Fifth Amendment applies to that.
If a civil motion is filed against you, and you do not respond, you have defaulted and in all likelihood the motion would be decided against you.
“The protection extends equally to civil proceedings because the nature of the protection goes to the questions asked, not the proceeding itself”
http://www.sualaw.com/papers/Fifth_Amendment_Right_Against_Self_Incrimination_in_Civil_Cases.pdf
In fact you might end up in the judges chamber, and he might tear you a new one. Or hold you in contempt.
But no finding of fact or law can be based solely, or even in part, on the fact that a person chose to not testify against himself.