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Did you try known good trackpad board/cable?
It can be a reason for full speed fan.
Does the fan spins to max from moment zero, or increases speed in 15-20s?
The above mentioned voltages took with machine turned on?
0.8V on CPU looks good; if drops from 1.15V initial.
However, you have a problem with SMC, or some of its signals; because PPBUS_G3H isn't controlled.
Check voltage and diode mode to ground at SCL/SDA lines of battery bus.
Remove internal HDD and test if stays on with USB macOS.
You can also test in boot menu.
Its showing very unstable behaviors. At first it didn't shut down with macos usb (i even installed catalina from usb and it didnt shut down), but now it shuts down with catalina and capitan install usb´s.
At some point i thought the wifi was causing the shutdowns since every time i tried to connect to wifi it shut down, so i disconnected the wifi cable and it started to show green light and regular fan spin (maybe just a casualty). But now its back to fast fan/dim green light.