Hi Floyd, Welcome to the forum and congrats on the "new" Sunline.
Most common would be corrosion in the light socket or a bad ground at the light. A shot of WD40 in the light socket with the bulb removed is one easy cheap thing to try. After that you need a cheap multimeter or test light to see if the 12 volts reaches the switch and then the socket, assuming the fuse is good.
Gene & DW Ginny
2002 Sunline T-2363
2008 Toyota 4-runner 4wd 4.7L V-8
Reese Dual Cam straightline - P3 Brake controller