Positive or Ground-Side switching?

[1991S13]

My stepdad just put Whelen UHFPOS headlight strobes on his government car, and he has a box left over that he gave to me to put on my car if I want. I figure why not, so Im going to hook it up.

My question is: the instructions say there are two different switching methods used to activate the headlights/parking lights; Positive-Side Switching and Ground-Side Switching. This product can only be used with positive-side switching, so can I use it? I don't know which method a '91 240sx would use, so hopefully one of you know.

Thanks.

[PoorManQ45]

For safety purposes you should ALWAYS use positive-side switching