The Stovebolt Site Forums The Shop Area The Electrical Bay Electrical Diagram Abbreviations

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!

I believe that NAT indicates the natural ivory color of the cloth covering. C.R. may mean cross, and like you suspected, T.R. means tracer. On the 1950-51 wiring diagram in the shop manual I have there are no periods between letters and that dimmer switch wire is labeled DIM. SW. FEED 12 GA. NAT BLK & RED CR. TR. I interpret that as as a natural cotton colored wire with black and red crossed tracers. A replacement for that wire is available HERE.

Why would Tracer be labeled T.R. instead of TR?

A period after each letter usually indicates two words. Same with C.R. I don't know the answer but by that logic, BLK should be B.L.K. etc.

You are correct, Otto, and that was an error on my part of writing the nomenclature.

on both versions of the wiring diagram its written as:
NAT. BLK. & RED CR.TR.
I agree TR makes sense that it means trace and is the alternate color for the wire. But I still don't understand CR. Some of the wires in the digram just have TR. with no CR.

And then I study the diagram some more and see another wire (for the high beans) the wiring diagram reads:
12 NAT. BLK. CR. TR.

With no alternate color listed as a tracer

also, confused about what "cross" klhansen means about cross?

so from this High beam wire description one might say that high beam wire is 12 gauge with the natural cloth cover with a black tracer.

Would that tracer be woven into the old cloth cover? I just looked at the one remaining piece of cloth wire on my truck (the wire down the steering column for the horn) and it's just natural with no detectable tracer color...that tracer could just be faded after 74 years, I guess.

The tracer is normally woven as part of the fabric insulation. It looks like hash marks all the way down the loom. In the case of my truck, the insulation is tan with various tracers such as red, black, red and black, blue, etc. The blue is hard to distinquish from black in my case even though the insulation and wiring looks almost new. The blue has darkened.

I will guess that NAT (natural) refers to the yellowish tan color of the cloth loom.

I don't think there would be any reason to label a wire as NAT with BLK tracer. All of the looms are tan (NAT) so the only color that is relevant is the tracer color, e.g RED, BLK, BLU, or RED & BLK

There are a couple wires on my truck that are plain w/o tracers. I don't think they could fade to invisibility. The cloth is died all the way through rather than printed.

I didn't see Kevin's reply when I made mine, above. I think the CR TR (cross tracer) refers to different directions of the tracer hash marks with red and black appearing alternate and perpendicular to each other along the length of the loom rather than red and black being alternate and parallel to each other.

There were wires with no tracer, wires with one tracer, wires with two tracers, and wires with crossed tracers (two tracers woven in the opposite direction.) See the attached pictures.

OK now that I looked At the original-style wires from Ton's I see what you mean about the "cross-Tracer." pictures worth a thousand words

Thanks for helping me figure this out as I am experienced at reading wiring diagrams and felt pretty stupid. I'm making A cross reference table for my truck to compare the correct wires from thew diagram to my actual wires (blue, green, orange, red with yellow stripe, etc.) to determine if the wiring is correct. I'm not doing a full restoration...just fixing bunch of stuff and getting this truck I've had 27 years back on the road.