Monitoring switch settings, voltages, temp and a-amps versus f-amps is a very helpful function when working on Gems.
Using it on T1, T2, and my tomberlin were plug and play.
T4 is another story.
Sentry does not communicate thru stock 23p plug.
This seems to be my next project.
Several hrs invested with little success. If anyone knows the key, let me know! 
Robert Meyer gave me a clue, but not enough to get it working.
It appears external switching and wiring is needed.
Another kit to build??
Worked most of the day with no success.
At least I haven’t smoked my T4 yet.
Big plans tomorrow.:clap2:
Got side-tracked when battery meter and some new boards came in.
Hope to get at it soon.
Success…:
:clap2: :
My dilemma.
Quite a complex rewiring job at T4 controller.
Lots of time and research in making monitor function work.
Simple in theory. Why isn’t this information common knowledge? Or is it?
I couldn’t find it!
If I just share what I’ve learned, there will be a lot of butchered Gem wiring harnesses.
Make some simple jumpers and leads with proper terminations?
Make a complete kit with a switch, switching from run to pc?
Either requires changes to harness. (reversable with proper terminations) It would make little sense to return wiring to original configuration, after programming.
Considerably more involved than the USB programming cable alone.
Will not be able to add it to cable, at no charge, as I hoped.
Can’t make it pretty.
Here’s the prototype.
5 leads must be replaced in 23 pin plug, which then plug into octopus.
2, 16, 17, 22, and 23…
No solder or crimp. Plug wires number to number.
Switch changes from pc to run/monitor.
Not practical to move from car to car.
3pin plug works with my standard usb to T4 device.
And for more diyers.
Mini kit for monitor only with your own programming cable.
Weather pack connectors and 23p terminals.
Not as intimidating. Also not complete.
This would be the complete kit. Including USB to T4.
Think I could build it for about $100.
Or 1/2 that for the add-on to my original cable.
No switch on this one. Plug-n-Unplug.
Looks better imo!
Opinions?