What do you mean, you are going to replace the underhood harnesses??
Have you downloaded a shop manual yet?
http://www.forabodiesonly.com/mopar/showthread.php?p=1970088617
http://www.mymopar.com/index.php?pid=31
68 service manual from MyMopar:
http://www.mymopar.com/downloads/servicemanuals/1968_Plymouth_Service_Manual.zip
Now, you have to use you head. Look at the diagram for the engine compartment, which in the above manual is on page 334 in your viewer, page 8-108. the diagram of the bulkhead connector. The individual connectors on the page which fit the bulkhead connector are looking INTO the connector, and the bulhead connector is looking at the bulkhead connector as it sits on the firewall
Now all the wiring for the lighting wiring is not shown on that diagram. But the top connector, which fits the left side, is the "lighting" section. The second one down (middle) is the "ignition" harness" and the last one down to the right, is your "wiper" harness