2: Keyless Ignition
With all of the other expensive audio upgrades that went into cars around the 2000s, keyless ignitions gained traction as well. Adding a keyless ignition to your car or truck was a great way to get it warmed up for you. Unfortunately, wiring one of these systems is very difficult and it caused a lot of reliability issues in certain vehicles.
Nothing is worse than having an electrical gremlin in your car and these keyless ignitions did that. Most new cars can be started from an app so the need for a custom keyless ignition all but disappeared for the most part.