I have read that the lower harness is not necessary to replace because it does not get as hot as the upper harness. Heat and humidity are what causes the bio-material made wire insulation to excelerate decomposition.

The top of the engine and near the MAF get hot as does the inside of the throttle actuator case. Humidity can include external and condensate.

I have read about the interior harness, but also not typical to replace.

I have read about the battery cable/harness being replaced, but I am not sure what that means.