This thread is documenting and sharing the research findings related to when the visible through the grill horn wires at the front of the radiator support. This is what I've collected and found so far. Hope it helps others with making their finished cars closet to how they were originally built.
For the early cars these horn wires each had a yellow with blue tracer line outer coating. Looking at all the cars we have available the color of the wires was later changed to an opposite color combination of blue with a yellow tracer that was not as visible and appears to have addressed the problem enough so that plants no longer needed to black out or hide the earlier style wire.
HORN WIRE #1
Now it's easy to mistake a prior owners rattle can clean up and the wires getting blacked out during process but often you will find remnants of black paint on other items in the same general area that should not be painted with black paint on them also. Eliminating the car as a good resource. Some examples of this below showing black paint on other items in the area.
HORN WIRE #2
I've yet to determine when and how long black paint was used for the purpose but it was a practice on at least some 65 Dearborn Mustangs for the same reason as San Jose Mustangs but Dearborn running changes is another subject. All the pictures of the four new cars below have what appears to be sealant applied to the area around the horn wire grommet.
HORN WIRE #3
San Jose also used the sealant that was used on the firewall to cover to the wires also. Once your aware of it it really can stand out on an original car
HORN WIRE #4
Here is a comparison of the spider web like sealant found on firewalls this year and the area around the horn wire. It was likely just added to the list of areas that needed the sealant and applied by the same worker at the same station. So far the product has only been found on the wire and radiator support as would be expected if applied that early in the building of the vehicle - before the horn was added.
At times you can find areas on top of the radiator support where the spray continued to, the daub started from or an accidental discharge - shown in the upper left of the following
HORN WIRE #5
As mentioned above, once the wire colors were changed there was no need to black out the wires and the practice of hiding them stop thought there appears in the research the message didn't get to the assembly line for a couple of weeks so some overlap - sealant on blue horn wires.
HORN WIRE #6
Since 1966 San Jose Mustangs and Shelby's had the later style wires the blacking out of the wires was not a factory practice from then on - through 70 when San Jose stopped producing Mustangs
Will follow up with a graphic of the research and the approximate change over range as usual.
