Howdy folks:
I have been searching in vain in this site (and elsewhere) to get a simple answer. I’m trying to decipher the abbreviations on the wiring diagrams for my 1951 GMC.
One diagram I’ve got is from page 148 of the “GMC Maintenance Manual 1947-1954” originally published in 1953 and the other is from the old car manual project page 12-3
As an example, both have similar abbreviated descriptions for the wire from the dimmer switch to the light switch like this:
12 NAT. BLK. & RED C.R. T.R.
Clearly this means a 12 gauge wire Black & Red but what is “NAT”, “C.R.” and “T.R.”
There are no “legends” on these diagrams.
I suspect “TR” is for tracer and refers to the secondary color of Red on a mostly black wire.
Would NAT indicate “natural” insulation (cloth and natural rubber)? The mice sure love that natural rubber, don’t they?
Of course none of my wires color original colors and a prior owner replaced cloth covered wire with plastic insulated but used whatever color they had laying around and I’m questioning if it’s even the correct gauge.
For the record, when I replace wires I stick with original color and gauge and have a set of paint pens I use to match the secondary color on the insulation so whomever ends up with my old cars won’t have to sort this out!
