The metal-to-metal contacts in the 1929-1957 MP&AC.
Group # 2.447 37-51 Switch Tail and Stop Lamp parts numbers 594904 and 594905
1952 was year, they went to spring-like conduit.
I can't find the spring-like conduit in MP&AC though.
It is in the FAM. factory assembly manual
Wire Assy. 55299935
sec.12, sheet 15.021 and 15.002
Photo 1Photo 2JC tech page scroll down.
After further review:
My hunch is from 37-51 the factory stamped indentations into the rear left barn door jamb and the rear left body jamb.
The indentations allowed the spring loaded plunger contacts in the door and the plate contacts in the body to be flush mounted in the jamb.
To save time and cost, in 1952 GM done away with stamping in indentations and using plunger contacts and started using spring type conduit.
To protect the wires from pinching in the jamb. The spring conduit actually slides into the door cavity when the door is closed, the spring conduit
is held in a fixed position with a grommet in the body jamb.
It would be interesting to see if the 1952 to 1955 1st series left rear barn door jamb and the left rear body jamb had the indentations.
xfiles