tail light relay problem...I think

I have a 92 Camry and I have a tail light problem. My break lights work fine when the break is pressed but when I turn my headlights on none of the lights in back turn on unless I press the breaks. I got to assume that it is a problem with the tail light relay or maybe some circuit breaker that needs to be reset. I've spent quite some time looking for the relays and I can seem to locate some of them that are in the haynes manual. If anyone could help that would save me a trip to the dealer. Thanks.