Aight guys, I finally crossed the finish line today. Thanks everyone for this amazing thread, and especially to
@TXSunDevil and
@BillZ260 for helping me with my troubleshooting. For those of you who were following along, I ended up rewiring the mag clutch wires, and cleaned the contacts on the controls. Pretty sure my controls just had bad contacts the whole time.
Here are my lessons learned:
1. "Cleaning" the HVAC controls isn't a soap and water or even air duster type deal. I initially decided mine were good after disassembling, as it looked brand new inside. However, it turns out these old controls have issues with oxidation/corrosion on the button contacts - causing them to be finicky. I would strongly recommend that you clean your secondhand controls prior to testing them. I used CAIG's Deoxit D100L with the needle tip and it worked wonders. I had no visible oxidation or corrosion from the start, but got 69% of my inop buttons back after one application, and a second application on two stubborn ones. They now all work. Some guy did a great writeup on FB on how to do it. If he hasn't posted it on MUD, I'm gonna get his permission and post that here so future guys can use it.
2. Don't remove ANY of your labels on the wires until you're 100% done and have checked every button. Even if you solder wire by wire like I did, not having labels to look back at seriously hampers your troubleshooting ability
3. I went with an Alpine ILX-w650 and a refurbished Kenwood X802-5. When I first installed them, I grounded the headunit to an extra ground wire on one of the old harnesses. That gave me a serious ground loop and lots of humming. In trouble shooting I realized that my battery to chassis cable was like 16ga, so my first move was to upgrade that. Got a premade 4ga cable from O'Reilly's for like $6.90 and slapped that bad boy on. Next did some research on why it happens. That drove me to take some 12ga wire and ground the headunit to the same chassis ground as the amp. Bam. Humming gone. Sanding down the paint where I ground it probably helped it be more conductive too.
4. When using the solder seals, I used the smallest sleeves possible to try and save room back there. Some of these connections were so tight that the wires only had room to be slid next to each other. That mostly worked fine. But I'd definitely recommend sizing up the sleeve if it allows you to wrap the wires around each other for a more solid connection. Also, I found my hot air rework station work great for melting the sleeves. Kinda like a nano-sized heat gun.
5. PowerProbes are lifechanging for electrical trouble shooting. If you plan on working on a lot of cars or doing electrical stuff in your future I can't recommend it enough.
Link to Deoxit:
Amazon product ASIN B0000YH6F8