Bed thermal runaway

Bed thermal runaway has put my Sidekick 239 out of commission. I have replaced the bed (new thermistor) with no improvement, so I’m assuming the problem is in the wiring harness. How should I approach the investigation? I DO NOT want to have to send it back to the factory. Thanks.

I’m not an electrical genius but with a multimeter you could ohm out each wire and see if you can identify which is faulty/broken?

Check the connectors on the board. They sometimes get burned out.