Tom, I bought mine on Ebay, but can’t find the same ones now. I will keep looking, and if I find them will let you know.
Tom,this what I used, it can switched from C to F . https://www.amazon.com/Digital-Temperature-Thermocouple-Sensors-Celcius/dp/B00V25HRA8/ref=sr_1_5?ie=UTF8&qid=1548910211&sr=8-5&keywords=12v+temperature+display+k+type or this https://www.ebay.com/itm/Digital-DC-Temperature-Meter-for-K-Type-EGT-Probe-with-Blue-LED-12V-F/380884091854?hash=item58ae7603ce:g:HsYAAOSw3pVZv2Vg:rk:12:pf:0
It most like won’t work by doing any mods. It probably senses buttons to turn on then shuts off after like 60x after last keypress. The best you could really hope for is a 555timer that you could unsolder, but it is highly unlikely. You might be able to find the number on the chipset and figure out how to reprogram it, but if it isn’t something common it could be really tricky.
You can also use an arduino or raspberryPi.