[Lilyree]

Need to replace my headlights and found some on a 2004 9-5 arc sedan. Will they fit?

 

[Doug]

If they're the same type of light (filament or xenon), yes. If not, I think it will be rather complicated. They'll physically fit but the control/monitoring systems differ.

 

[Jeremy R.]

There have been a fair number of people who have replaced HID headlights with halogens to avoid the complexity of the system, so there is a way to bypass the HID monitoring system, at least. Adding all of the HID parts to a car not originally equipped with HIDs is probably beyond the abilities of most people, but if you're installing Arc headlights in an Aero, you're probably either replacing HIDs with halogens or replacing HIDs with HIDs.