Bulkhead Disconnect Plug - Wire Change?

Sure. Both male and female have little "tongues" that latch into the plastic. Generally, a very small screwdriver. These are called "Packard 56" terminals Here:

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The male end works a bit different. The odd looking "leg" is the latch, you must reach in and bend that a bit to release the terminal

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I switched the whole engine harness on my 68 dart with a harness from a 73 duster. Had to swap one wire. I need to replace the harness I used or buy a new one but can’t seem to find one with all the bulkhead connectors. Where can I get those at. Thank you.