First thing, the appraiser only did a preliminay visual inspection for the estimate. This does not mean that it is a full and final payment. Take your vehicle in to a Dealership you trust, they will will have to start a teardown and will contact the insurance company for a supplement. A wiring haness is considered and OEM saftey item because it controls so many engine functions and a repair failure can cause and accident or fire. Speak with your adjuster after a supplement is completed if they say it can be repaired. Most adjusters have very limited automotive knowledge, and bring up the safety issue that way it will be documented in the file. The last thing an insurance compay wants is a claim that due to their insistance of repair causes a fire or accident because the exposure is huge. Just dont threaten to get a lawyer because adjusters hear that every day, this claim is different because you are the insured so they have a contractual obligation with you. If the rodent damage is minor and the OEM states that the harness can be repaired and there is a published repair proceedure, it will be repaired, but if the OEM states it cannot, the insurance company is obligated to replace.