Sleepwalker,

If there is a fault in the wiring harness on a C280, will it show up in the HTT/ Star Diagnosis?

 

it depends on what is affected.

the fault can be stored or present.

it won't tell you the wiring harness itself is faulty.

eg. the connector on the temp sensor is loose or short to ground... it will only say: temperature sensor is faulty (out of tolerance).