Thanks to all for your advice / comment.
The RV dealer pirated a socket from a new tail light assembly, screwed it into the base of the light, and, IT WORKED.
He called 6 places in Wichita trying to find the piece that Roy recommended, but none carried them. Had I had more time I would have ordered one from e-bay but time being of the essence, the dealer's improvisation would do.
Turn signal works like a charm, and I tooled on down the road to Tucumcari today,signalling frequently, just because I could