97 Chevrolet K1500 tail lights

I have a 97 Chevrolet K1500 that I bought new.  
After 315000 miles the engine died and it sat for
four years.  After new motor and tranmission
everything works flawlessly except tail lights.  
When the lights are off i have very weak blinkers
and brake lights.  When the head lights are on I
have nothing at all.  When the emergency flashers
are on and the head light switch is off I have
flashing tail light as well as tag lights..  I'm sure a
rat has chewed my wiring but just want to know if
anyone has had a switch cause this kind of
problem.  Thanks in advanced for any help