The rear lights are not working, but the signal lights work, what's wrong?

No voltage is going 'through' the bulb elements to make them glow!

"rear lights"-----tail lights or brake lights?

Tail lights,brake lights and turn signals are on separate circuits although they may share the same ground. Check fuses and bulbs first. Then take to a competent mechanic.

Saturn L200 Recall 05V245000 Recall 05V245000 Electrical & Lights, October 17, 2005 Original Recall from the NHTSA Model Year(s): 2001, 2002, 2003 Manufacturer's Report Date: October 17, 2005 NHTSA CAMPAIGN ID Number: 05V245000 NHTSA Action Number: PE05010 Component: EXTERIOR LIGHTING:BRAKE LIGHTS Potential Number of Units Affected: 291,652 Summary: ON CERTAIN SEDANS AND WAGONS, THE PLASTIC HOUSING IN THE REAR TAIL LAMP ASSEMBLY CAN BECOME DISTORTED IF THE BRAKE LAMPS REMAIN ON FOR AN EXTENDED TIME. Consequence: THIS CAN CAUSE (1) AN INTERMITTENTLY INOPERATIVE BRAKE/TAIL LAMP BULB OR (2) A SHORT CIRCUIT THAT OPENS A FUSE CAUSING INOPERATIVE BRAKE LAMPS (INCLUDING THE CENTER HIGH-MOUNTED STOP LAMP) OR TAIL LAMPS. A FOLLOWING DRIVER MAY NOT KNOW WHEN THE BRAKES HAVE BEEN APPLIED, AND A REAR-END CRASH COULD OCCUR WITHOUT PRIOR WARNING. Remedy: DEALERS WILL INSTALL TWO NEW TAIL LAMP REINFORCING SOCKET ADAPTERS AND SOCKETS FREE OF CHARGE. THE RECALL BEGAN ON OCTOBER 17, 2005. OWNERS MAY CONTACT SATURN AT 1-800-972-8876. Notes: GM RECALL NO. 05052.CUSTOMERS MAY ALSO CONTACT THE NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION'S VEHICLE SAFETY HOTLINE AT 1-888-327-4236 (TTY 1-800-424-9153), OR GO TO HTTP://WWW.SAFERCAR.GOV.  Recall data provided by the National Highway Traffic Safety Administration