I have a 1978 Olds Delta 88. My running light's in the rear do not work. The front's work fine, of course. The brake and turn signal's work in the back, so do the reverse light's, but no running light's or license plate light's. Can anyone tell me what they think it might be, cause i know nothing about electrical and cannot drive at night anymore. It's gotta be something stupid or simple!

Thank you and god bless...