Aftermarket harness.

IDK. They're pretty useful providing a compact, organized, and secure method of pass through.
They allow relatively easy diagnostics and isolation of individual circuits and wires.
The opposite alternative would be a cable bundle through the firewall, properly secured with insulation, yet allowing no movement which could cause were or chafing.

Starting from scratch you could do a thoughtful combination of both methods.
I've noticed that where Chrysler did use grommet feed throughs they often provided some sort of in-line wire connector nearby.