Plugging anything into Thunderbolt inc bare cables causes kernel task overload I have a 15" Late 2013 Retina MacBook Pro (2.6GHz Intel Core i7, 1TB SSD, 16GB RAM), and have been trying to solve my kernel task nightmare for years.  

I've read every article and forum post on the Internet and tried it everything, including deleting kexts, resetting RAMs, cleaning dust out of fans, replacing the battery with a new one, applying new thermal paste to CPU, running apps that check for faulty thermal sensors, malware, and many other small recommended fixes. Nothing has ever worked and I've been on the brink of just giving up and getting a new computer that works consistently but I took a final stab at trying to diagnose myself.

Through careful monitoring and note taking, I've found that it only happens when anything is plugged into either of the two Thunderbolt ports. I personally have tried a few different external hard-rives on a firewire to Thunderbolt adapter and also a Thunderbolt recording sound card. What I've found is that I can create a positive kernel task overload by only plugging in the bare cables with no actual device on the other end, even connecting only the adapters by themselves creates an overload. My audio sound card is a straight Thunderbolt 1 cable connection (no adapters) and this also creates the overload.

This follows with countless people I've read who have the kernel task issue using Thunderbolt displays and Thunderbolt ethernet adapters. And it seems that everyone is addressing their particular devices when it seems to be the Thunderbolt ports as a whole, which I actually haven't seen addressed anywhere so I'm starting it here.

If anyone has been struggling with this issue, keep an eye on your Activity Monitor while alternating devices and cables into your Thunderbolt ports.   I'm not sure if its important to note that kernel task overloads are mostly, but not always, showing as the actual kernel_task process itself in Activity Monitor, sometimes any random program that I have open such as a Web browser or DJ program will hover to 500% usage until everything is disconnected from Thunderbolt instead.

I would love to find a real solution. I've never had any physical damage to my MacBook Pro, but would replacing the logic board or any other board fix this?
I've actually had the same issue forever with my mac. The same device as yours.

I took it in to get fixed just before my 3 year warranty expired and unfortunately I thought it was fixed, but it wasn't. (Very regrettable that I didn't notice it wasn't resolved till after the extra 90 day warranty had expired.) 

I honestly think it's a defect in the device, but have no idea how to fix it. I've tried many solutions over the years and just found your post as I'm restarting my search.

It is so frustrating to not be able to use the second monitor I have sitting here.

Not a solution, but one thing that helps a little with the kernel overload is running an actual fan across the surface of your computer.

If you've come up with anything, please do share.