How and why is there a sharp, masked paint line on the interior of the firewall? No paint on the top half and underside of the cowl. Is this for ease of grounding or something? It definitely took effort, which means it was done for a reason.

This is in my '68 Charger...

The completed main bodies after major assy, went into a series of "baths", the primer dip being the last before going off to paint, that's the reason for all the floor body plugs, to drain the chassis after dipping

Looks like a "dip" line. The lower part of the body went through a dip tank to rust proof the body at the factory.

Illustration showing the dip process at http://www.hamtramck-historical.com/imag...neering0010.jpg

That doesn't explain why that line seperates bare metal from color coat. Regardless of the dip there should at least be overspray above the dip line.

Here a picture of an original T/A

Why would there have to be a color coat above the dip line ???Looks like the color coat barely made it to the dip line let alone painting much past it on the other examples...I'm thinking the color coat is a close match to the dip primer and the overspray was enough to tint the primer making it appear it's a taped color coat line...

In the op's photo it definitely looks blue up to that line. Was the dip blue? Not on my car! It just looks like bare metal.

Unless it was blue primer...

That it a hard line there. If you look above the passenger cowl vent opening, there is some blue overspray with some glue and insulation stuck on it.

The factory was using blue primer now ?!?!?!?

Prior to dipping I assume.

I think maybe the flash or lighting makes it look more blue than it really is.Looks very close to Resto Ricks primer dip formula.

67charger is the body blue also,is the firewall paint primer like or body paint,sure looks like a dip line to me higher on the R/side then left.

My 69 RR had a pretty dark gray dip.
I'll have to look closer at my coronet.

I'll go snap another picture. It is the exact shade of blue that the car is and was, just not glossy.

Got to be a dip line. It is quite close to blue, but it must be just enough blue matallic overspray to make it look like dull blue paint. Seeing the floor and door in the same picture puts it back in perspective.

Of course it's a dip line. It's probably in the trunk too, as well as on the wheel tubs, the diagonal braces behind the rear seat, and on the inner quarter panels.