So now we have a final layout with lots of real-estate in the cabinet still. The THC is easy enough to waterproof, an end-cap for the connector side is presently being printed (15-hour print). Now to drill some holes, read Tom’s stuff on Z calibration and on to getting all those colored wires connected. Long weekend here, so stocking-up on beer and getting down to the build. 
Power-up test went well, no magic smoke seen anywhere! 
Water-resistant shield/endcap for the connector end of the THC3T. Since I don’t have black filament, it will be bomb-sprayed flat black before installation.
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I don’t know. I think the gold color has a certain je ne c’est quoi about it that seems like it could work. I think you should try it as is.
That printer is nice and tight. What printer is it?
Ender 3 pro
Power failure about 12 hours into the print. Luckily, I designed it 1/2" longer than necessary. So, salvaged it!
Progress report:
It’s alive! I’ve got all the necessary power connections done, and isolated the USB power. Got the X and Y axes connected and set the dip switches as per the OEM configuration. Happy to say so far so good, presently it works exactly as the OEM control box, no blue smoke.
So,now the focus is on building the Z-axis circuitry. Will have a fresh beer to celebrate and then hit the sack!. At the crack of dawn, Z-axis here I come!
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Hmmm, where do I find this?
Well, I didn’t intend it to sound bigger than it is, but it’s in Finally completed my CrossFire mods - #11 by TomWS, about halfway down,
The main point is to cable it so that you can wrap the two cables together to feed the Z Stepper directly without the THC controller messing you up.
Ahhhh! ok cool!! …I’m at that point in wiring now.
Ok, so, is the general wiring diagram I should be using to inter connect the THC? (i’m using the 50:1 divider so I know that will be wired to the other terminals)
I’ve seen a couple variations and a now little confused.
Yeah, it took a while to figure out. I still have my chicken scratchings but I don’t dare post those. I’m redrawing now, be back in a couple…
Don’t stress out over it, we accept finger lickin’ Chicken Scribblings!
This is where I’m at (Gnd, +5 and +24 to the THC going in now):
RB 2020-08-29 11.34.26.pdf.dxf (146.5 KB)
Ok, so there are 4 connectors in the system, one for the Z stepper, one for the CF controller signals, and two for the THC, one input one output. The connectors are mating where the Z Stepper is a plug and CF controller a socket. Same thing with the THC connectors, inputs are plugs, outputs are sockets.
Connected with THC in place, that CF connector goes to the THC input and the THC output goes to the Z stepper. Bypassing the THC, you simply connect the CF connector to the Z Stepper.
The only thing that’s sort of funky is that the THC In GND gets connected to the ARC OK GND. This provides the return for the ARC Ok. I don’t use this signal at all, but the connection is there.
Note that the THC In + pin isn’t connected to anything. It’s there only so the CF + pin can drive the Z Stepper plus if you’re bypassing…
GREAT! …Mulling that over now!
Thanks, will holler at the first signs of blue smoke! 
Thanks Tom!
OK, that took a bit of concentration!
But its done, no smoke, lights be lighting and fans be fanning!
Now to mount limit switches and the Z-axis on the table.
The cabinet is essentially done!
BTW I like the ability to bypass the THC altogether if necessary.
Same mount system for both cabinets, the OEM and Mine, makes for easy changeover using two 3" x 1/4" bolts and wing-nuts.
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Yeah, you probably want to bypass initially until you’ve got your Z settings tuned. You’ll need that info (plus some trial cuts) to setup the THC registers.
Understood.
I just hooked up the z in bypass mode. Works fine. Will try to do a cal tomorrow. Machine torch from George coming in next week… more toys in the cave! 
Ah ha! …I may have encountered one little snafu! 
In bypass mode I can jog the z up and down just fine. In THC mode I can only jog the z up, it does not respond to down. Probably a direction signal issue somewhere. Will dig into that tomorrow when I’m less tired!