Head light pop up on they own???

[Mark6]

82 mark vi head light flips up by they selves after sitting for a day or 2, what causes this?

[Mike]

It's a safety thing. You'd have to check the service manual but I think those use vacuum to close them and if there's any leak they'll default to popping open rather then closing in the dark when you need them.

[papawayne]

Be grateful it's only a day or two. All if these cars have this same vacuum problem. They go closed as soon as you start the car, right? And they work when it is raining or dark, right? The good news is that judges at an LCOC event only want to see them work, they don't care how many months they stay closed. Wayne

[Mark6]

It's a safety thing. You'd have to check the service manual but I think those use vacuum to close them and if there's any leak they'll default to popping open rather then closing in the dark when you need them.

Wow really it's a safety thing? I always thought it was a slow leak in a hose or something

[Mark6]

Be grateful it's only a day or two. All if these cars have this same vacuum problem. They go closed as soon as you start the car, right? And they work when it is raining or dark, right? The good news is that judges at an LCOC event only want to see them work, they don't care how many months they stay closed. Wayne

Yes you right, it closes right up when car is started

[Lee]

Wow really it's a safety thing? I always thought it was a slow leak in a hose or something

What that means is, if there is a vacuum leak, the lids will open. Open is the default position. If the default position is closed (like my Cougar), if there was a bad leak, you wouldn’t know until you turned your headlights on, and the doors don’t open.

[Mike]

Yes. Your problem is you have a leak. It's a safety thing that they open on their own if it leaks.

[Dan Szwarc]

It’s usually a faulty check valve and can also be a cracked headlamp switch in the vacuum switch portion.

[Mark6]

Is there any diagrams? Was trying to find 1 online, where's the check valve located

[Lee]

Here you go.

[TonyC]

It could also be something simpler, like a hose that has become brittle with age and can no longer seal vacuum. It could be split at a fitting end, or broken at any spot, or just hardened. The tricky thing is finding the cause.

If the components like the headlight switch or check valve are sound, then it has to be a bad hose somewhere in the engine bay.

---Tony

[Mark6]

Thanks Lee for the diagram and Tony thanks you right something could be brittle I'm definitely going to go over this weekend while I'm off

[Dan Szwarc]

The check valve is going to be in-line with the vacuum source (engine or vacuum tee) and then tee into the storage and the main headlight system. It may also be the tee itself with the center line going to the source,

It prevents the system from losing vacuum when the engine is off.

If this doesn’t make any sense, think about how vacuum works or find a detailed vacuum manual.