To contest a traffic violation for running a red light in California, plead "not guilty" to the charge and pay the ticket fine. The court then issues a trial date regarding the infraction.
California drivers contesting traffic violations are always allowed to hire traffic ticket attorneys. You also have the option of representing yourself in court. At the trial, you may question the arresting officer, argue the points of law, and present evidence and witnesses. If the verdict is "not guilty," the initial fine paid is refunded to you. If the verdict is "guilty," any remaining fine must be paid.