Where is the location of headlight relay switch on 1999 Cadillac deville?

The headlight relay on a 1999 Cadillac DeVille isn't a single, easily accessible switch like in some older cars. The headlamp system is controlled by multiple relays and components within the Body Control Module (BCM) and underhood fuse/relay center. There isn't one specific "headlight relay switch".

To find the relevant relays, you'll need to:

1. Consult your owner's manual: It should have a diagram of the fuse and relay box locations and what each relay controls.

2. Locate the underhood fuse and relay center: This is usually a black plastic box under the hood, often near the battery.

3. Inspect the relay box: The relays are usually small square or rectangular components that you can pull out and examine. Your owner's manual should help you identify the relays associated with the headlights (they might be labeled, or you'll need to trace the wiring).

Important Note: Problems with headlights on a 1999 DeVille are *rarely* due to a failed relay. More common causes include blown fuses, issues with the BCM, wiring problems, or a faulty headlight switch itself. If you're having headlight trouble, it's best to start by checking fuses first, then consult a wiring diagram to troubleshoot further. Trying to replace relays without understanding the system could lead to more issues. A qualified mechanic will have the proper diagrams and tools to diagnose the problem correctly.