Clicking noise

[emorse]

1991 year. When ignition is turned on (engine not started) I hear a consistent clicking noise from the engine compartment. Stops when vehicle started or ignition turned off. Thoughts from anyone? Thanks.

[Karl]

Air pump for the secondary fuel injectors?

Is it coming from under the passenger side headlight?

[emorse]

using a stethoscope sound is heard most near brake lines at the front wheels.

[mlipmd]

Secondary vacuum pump, underneath the PS headlight near the coolant tank. It should only run for a few seconds on initially turning on the key, then shut off and run a few sec. a short while later. If yours is running continuously you have a vacuum leak you have to find.

[emorse]

Thanks.