While I can certainly appreciate your request, there isn't a "one size fits all" answer. Modern cars now have (frequently multiple) digital communications networks within them. These are used to move much more information (think NAV, ABS, stability managment, audio controls, throttle position, etc.) between the many electronic modules. In turn, they save a tremendous amount of point-to-point copper wire (expensive, bulky, heavy..) The most common of these automotive networks is the CAN bus. These pass through many different connectors throughout the vehicle. A disruption in any one of these will raise all sorts of havoc as you have observed.

Fortunately manufacturers have been smart about this. These connectors almost always have latching mechanisms - once _fully_ inserted, they can't back out without first releasing a safety catch. CAN bus uses a twisted pair of wires and is smart enough to enable continued (though possibly degraded) operation if one wire or the other is open or shorted to ground or 12V. Each module that "talks" on the bus implements it's own self-diagnosis procedure to virtually ensure that a faulty module can not saturate the bus with garbage data -- they will take themselves off-line if they repeatly fail to properly deliver their intended message.

When a vehicle has problems with one of these busses, the dealer is able to run diagnostics that tell them which modules are performing properly and which have disappeared from the bus or failed. Most modules even store their own fault codes for after-the-fact diagnosis.

I think you will find that these kinds of problems are relatively rare and in those rare cases easy to diagnose and resolve in the case of something like a disconnection in the wiring harness.

On the other hand.... I could relay exasperating stories about a 2 1/2 year intermittent problem on one of my vehicles that was finally found to be caused by a K-bus (not as sophisticated as CAN) wire that had rubbed against a dashboard support brace and was intermittently shorting to ground. I taught myself more about K-bus than my dealers techs will ever know, and between us could not exorcise the demon until the insulation in a second wire in the harness wore through and shorted. That caused the 4 way flashers to start turning on and off on their own free will! Fortunately that provided two issues to trace to a common location since the K-bus had nothing to do with 4way flashers.

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L8apx