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82 Mark VI Hissing Sound

Hi Bill -

I have a '82 Lincoln Mark VI and a have a vacuum leak hissing sound only when the headlights are turned on from under the dash by the headlight switch. The headlamp doors work when turned on and holds vacuum when turned off. But it does have this constant hissing sound when turned on either by the autolamp or headlight switch. Is this the vacuum box or a escape valve?

Thanks for the help,



Hi Rick -

So it's the old vacuum hiss trick. These can be annoying and sometimes hard to find but if you can hear the leak as you can, it shouldn't be too hard to find at all. We would start by inspecting all of the vacuum hoses under the dash that operate the Headlamp doors. A hose may have fallen off or been inadvertently knocked off during a previous repair. The Autolamp Module or vacuum box as you call it could also have a hose off inside or the H/L switch vacuum portion could have self destructed. Keep in mind that vacuum can leak anywhere that the vacuum is routed to and for this reason the leak could be actually found under the hood at any location where the hoses are fed to. Many times with a large remote leak the driver hears the vacuum rushing through other components under the dash as it speeds toward a leak that is located under the hood etc. This fools us into thinking that the leak is close by. All of the above is based on our past experience and scenarios Your problem should be easy to locate. Another possibility to consider is when did this leak begin? If you remember that it started immediately after a repair or service to anything near this vacuum circuit, I would start at that location. If you find that you need any parts, we usually have them in stock as well as the necessary service manuals for your car. I hope that the above leads you to a speedy and simple repair.

Sincerely -

Bill and all of us at Lincoln Land