Solved Printer reporting over temperature when extruder is off and cool

So here's the sequence....

Removed the hot end to clear a jam and do a cleaning. All goes well. Go to put it back in place and I get this error:

->Communication State: Connected

<-echo:Marlin1.0.0
<-echo: Last Updated: Apr 28 2017 16:10:13 | Author: (RoBo 3D, R1+ Single Extruder)
<-Compiled: Apr 28 2017
<-echo: Free Memory: 3952 PlannerBufferBytes: 1232
<-echo:Stored settings retrieved
->M115

<-Error:0
<-: Extruder switched off. MAXTEMP triggered !
<-Errorrinter stopped due to errors. Fix the error and use M999 to restart. (Temperature is reset. Set it after restarting)
<-echo:SD init fail
<-FIRMWARE_NAME:Marlin V1; Sprinter/grbl mashup for gen6 FIRMWARE_URL:https://github.com/ErikZalm/Marlin/ PROTOCOL_VERSION:1.0 MACHINE_TYPE:ROBOR1PLUSV2 EXTRUDER_COUNT:1 UUID:00000000-0000-0000-0000-000000000000

Now it's off and cool to the touch but reporting a temp of 357.5 C. Luckily I have a spare extruder, so thinking it's a thermocouple issue, I swap it out. Same result.

Typing M999 just gets this:
->M999

<-Resend: 1
<-ok
<-ok
<-Error:0
<-: Extruder switched off. MAXTEMP triggered !
<-Errorrinter stopped due to errors. Fix the error and use M999 to restart. (Temperature is reset. Set it after restarting)
->M105

<-ok T:357.5 /0.0 B:26.3 /0.0 T0:357.5 /0.0 @:0 B@:0


Suggestions?

 

Its stuck in the error so no jiggling required. As I mentioned, I even swapped out the hot end (different thermocouple) with the same result.

 

Ok, so jiggling didn't work at first but...

I checked the resistance on both thermistors and they were ok. So I plugged the original back in, carefully, and it worked. Jiggling it around, it sent back to the error condition, and after another jiggle life was good.

So what's the answer? Bad connector? Bad wire? What should I be replacing? I'm not confident that if I get it to somehow work that it will continue doing so.