Electrical help needed, underdash wiring is a disaster

It's difficult with the dash in the way, but the entire dash was designed to be installed easily when originally built. You can take the entire dash assembly out, and work on it from the back side.
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I disagree that complete dash assembly is easy to remove for the simple reason to remove it, the dang windshield needs to be removed. That’s a non-starter for a lot of people! I agree that when it’s on the bench, then it’s a piece of cake to get at everything.