The sequential portion of the VIN is the last six digits, so I'd like to see one more digit, but even if it is a "one" that would make it 140018.
VINs for Chevrolet trucks in 1978 started at 100001, which would make this around 40,000
Chevrolet units in. Additionally, GMCs often had their own VIN sequence, starting at 500001 (for example) and would be interspersed about one every nine or so vehicles inbetween the Chevys, on the same assembly line, pushing the build back further.
Just a couple other considerations for conversation purposes:
a) VINs do not indicate build sequence. The General Assembly sequence number is what tracks that value, but is not recorded and therefore typically lost to history. The VIN numerical portion
is assigned sequentially, but within other constraints like nameplate based on the receipt of the order number at the specific plant. It's not too bad if it is just Chevrolet and GMC, but if a plant is building Buick, Olds, Pontiac, Chevrolet and Cadillac all down the same line you can see how the VIN would diverge quite rapidly from an actual build sequence indication.
b) There is no correlation between VINs at the various assembly plants. Each plant increments up based on its own production cadence (basic line rate, overtime, extra production days, holidays, downtime due to material shortage or other disruptions) with no relationship to any other plant. There were about seven final assembly locations building squares at this time, with Flint Assembly typically being the "lead" plant when it came to new product launch (due to its proximity to Chevrolet Engineering and Chevrolet "Headquarters").
I would guess your truck was built about 45,000 or so units into the 1978 model year for that specific assembly plant (which you did not name).
Probably a bit late in the model year to attribute it to any kind of "new model" blues. Those are usually ironed out within the first few days of production start up.
My guess is the operator grabbed the wrong part for the truck and when he/she realized the mistake just pitched (or dropped) the part on the floor, and then installed the correct part, especially since the part you found would be the "base" (or the "default") part and would be the part to be installed 9 times out of 10; the pulse wipe switch would be optional content. Pulse wipe was available in both '78 and '78 so it's not like it was new content.
Pulse Wipe is RPO CD4 ("Windshield Wiper System - Intermittent"):
https://www.gmheritagecenter.com/doc...olet-Truck.pdf
K