I finally got off my duff and replaced my original Mk2 sled with my spare Mk2a sled. Several of the crimps on the Mk2 sled had apparently gone bad, and I'd have speakers coming in and out, power going in and out, etc. Enough of that. My dad and I wired everything together with the never-before-used Mk2a sled, and everything's been working great for the front channels but the rear is flakey. If you wiggle the rear channel wires where they come into the wiring harness, the rear channels pop in and out. We tried all the usual process of elimination, and it's clearly a problem with either the crimp or with something at most 1cm beyond the harness.
What's the fix for this? Is the wire harness end-user servicable? Do I just need to drip a bunch of hot solder into the appropriate crimp areas? Other ideas anyone? The whole point of this upgrade was to finally have all my connectors stable, so I wouldn't fear driving over bumps in the road. *sigh*