Headlight operation??

[LannyL81]

My question is regarding the headlight switch under the dash...you know the pull-down vacuum switch that is supposed to open and close the headlights with the engine off....mine does not, all I get is a very small movement and then they stop. So I assume that I have a vacuum leak somewhere. I have checked all the connections in the nose...cannister holds vacuum..no holes there..rubber hose connections all seem tight.....inspected hose all the way back to the T's and check valves....all the way to the intake manifold. Took out the right angle fitting and put more Teflon tape around the threads and put it back. Used a hand vacuum pump to check all the lines and never found a leak.

Anyone have a suggestion as to where to look from here???

This leak may also be the reason why I am running so rich.

Thanks,
Lannyl81

 

[bill81vette]

Lanny,mine only works with the engine running,I didn't know it was supposed to work with the engine off,I just figured it was for opening and closing the doors without the lights on...If I want to open them or just one I reach down under the front bumper and pop it open (or close it) by hand....

 

[redvett]

The pull down valve is only intended to work when the engine is running and creating vaccum. You probably have a vaccum leakbeing the car is 25 years old unless you have already replaced components. I would check out the check valve close to the vaccum fitting on the line. Thats the first to go.
A vaccum leak will cause a carburetor run engine to run lean. You have a Q-Jet carb. and either the float is bad or the plugs in the bowl are leaking.

 

[Peer81]

Did you check the seals in the headlights themselfs? In the actuators or how do you call them?

Groeten Peter.

 

[LannyL81]

According to the 81 Service Manual, the vacuum pull-down switch is supposed to open and close the headlights with the engine off two or three times before depleting the vacuum.
The Haynes manual states that the headlights are okay to open by hand, but never closed. Didn't make sense to me.

Checked the check valves at the intake, but was not able to get a good enough seal with my hand vacuum pump to do the headlight actuators and vacuum switches. Have to get an adapter and try again.

And yep using the QJet, but I thought a vacuum leak would cause a rich condition...oh well....waiting for air horn gaskets to arrive so I can really check the float level....its got to be off.

Thanks,
LannyL81

 

[Vettehead Mikey]

According to the 81 Service Manual, the vacuum pull-down switch is supposed to open and close the headlights with the engine off two or three times before depleting the vacuum.

That's correct and it applies to all C3 Corvettes. Over time, they develop leaks (could be just about anywhere) which lessens the ability to hold a vacuum after shutdown. A 100% perfect system will hold vacuum for 24-48 hours and still be able to open and shut the lights at least once.

 

[Vettehead Mikey]

This leak may also be the reason why I am running so rich.

A vacuum leak will cause your engine to run lean, not rich. Try unplugging and blocking off the headlight system and see if your engine behaves differently.

 

[redvett]

According to the 81 Service Manual, the vacuum pull-down switch is supposed to open and close the headlights with the engine off two or three times before depleting the vacuum.
The Haynes manual states that the headlights are okay to open by hand, but never closed. Didn't make sense to me.

Checked the check valves at the intake, but was not able to get a good enough seal with my hand vacuum pump to do the headlight actuators and vacuum switches. Have to get an adapter and try again.

And yep using the QJet, but I thought a vacuum leak would cause a rich condition...oh well....waiting for air horn gaskets to arrive so I can really check the float level....its got to be off.

Thanks,
LannyL81

Throw thew Hayes manual away there not accurate the factory Heims manual will tell you everything you need to know to repair.
The vaccum tank in front of rad support usually has had leaks.
When you remove carb take the throttle body off the float bowl assembly and neal over all the lead plugs lightly with a very small ballpeen hammer. This is where the fuel leaks into the manifold. If you have a hard time starting up after a few days of sitting than the bowl is drained dry and is leaking. You should have gotten a rebuild kit it has all the gaskets. If any gaskets stick just soak with WD-40 for a while and carefully disasemble.

 

[LannyL81]

Operation description

Can someone tell me where to find a description of the operation of the headlight vacuum system? My real question, is what is it that tells these relays to switch so that the headlight close? It has got to be the removal of vacuum from the opening side of the actuators through the LIGHTS switch...is this correct?

I can apply a vacuum to the white line going to the relays and it holds vacuum. But at the sametime I do not get vacuum to go to the canister. I have checked the canister itself and it holds just fine. I am guessing that the relays need to switch but have not figured out what causes this action yet.

Somebody has got have gone through this already and is willing to share???

Thanks to all.....
LannyL81

PS The Haynes manual is normally only used to level out a table leg!!

 

[bill81vette]

there is a relay/valve of some sort on the headlite switch,I noticed it last year when I changed my switch,
Are your lines in good condition???(No cracks ect)If they are all ok It has to be somewhere else,relays leaking,headlite actuators,or whatever,to me its not a big deal.I just work around it.
If you do track it down I would like to know the fix so I can do it to mine and put it on my list of things to fix.

good luck

 

[LannyL81]

Headlight operation figured out

Got the headlight operation figured out. Really quite easy...once I took another look and saw that there are two vacuum lines going up front instead of just one.
There is the vacuum source that goes to the canister and then their is the vacuum line that goes to the vacuum switches.
Applying vacuum to the switches and guess what....they switch. This vacuum comes through either the headlight switch or the pull-down switch.

I am going to try plugging the headlight vacuum source coming off the intake and see what difference it makes regarding how the engine runs. Also going to try cutting the ends off all the hoses up front to get unstretched rubber connections....may be even new clamps.

Later,
LannyL81