headlight bypass switch not working, hissing
Thread Starter
Instructor
Joined: Oct 2010
Posts: 140
Likes: 0
From: Sunshine Coast Queensland Australia
headlight bypass switch not working, hissing
The pull down headlight overide switch worked great until the car went to the mechanics and had headlights replaced for oz conditions. Now when i pull down switch with engine off air hisses through the switch. When i reverse the hoses the switch doesn't his and headlights go up only when engine is on. I have taken the switch out and it looks new and headlights are now stuck up. Where do i start looking for a crossed hose as its tight under the hood and there's stuff going everywhere. I am sure its an easy fix but i don't know where to start.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Your system is the easiest of all. Go to this link and look at the first diagram,you should be able to see where the problem is.
http://forums.corvetteforum.com/c3-t...tem-works.html
http://forums.corvetteforum.com/c3-t...tem-works.html
Thread Starter
Instructor
Joined: Oct 2010
Posts: 140
Likes: 0
From: Sunshine Coast Queensland Australia
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
The pull down headlight overide switch worked great until the car went to the mechanics and had headlights replaced for oz conditions. Now when i pull down switch with engine off air hisses through the switch. When i reverse the hoses the switch doesn't his and headlights go up only when engine is on. I have taken the switch out and it looks new and headlights are now stuck up. Where do i start looking for a crossed hose as its tight under the hood and there's stuff going everywhere. I am sure its an easy fix but i don't know where to start.
What is the problem your trying to fix,start with everything hooked up correctly?
Headlights don't operate using the headlight switch ?
Hissing with engine running ?
Headlights stay up ?
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Burning Brakes
Joined: Apr 2009
Posts: 807
Likes: 2
From: VIRGINIA BEACH VIRGINIA
The headlights will only go up with the car on. If you shut the car off with the headlights still up, they will stay up and until you re-start the car. You should not hear a hiss at all under the dash whether the switch is pulled or not. I am thinking you have a hose that was knocked loose under the dash or right inside the engine compartment. look at the bypass switch real close, it may have a crack in it.
....ROGER... knows all so answer his questions and he will fix your problem.
....ROGER... knows all so answer his questions and he will fix your problem.
Thread Starter
Instructor
Joined: Oct 2010
Posts: 140
Likes: 0
From: Sunshine Coast Queensland Australia
O.K, I will try and explain this as clearly as possible.
It's a 1975, everything was working good until the car went to the mechanics and had the low beam headlights replaced for Australian conditions.
Now the headlight overide switch does not work and hisses when pulled down.
When the headlight switch is pulled out (with engine off) headlights do not pop up.
When the bypass switch is pulled down, headlights do not pop up and i can hear hissing coming from the switch. The switch looks new, as do the hoses and both switch and hoses are colour coded and are in correct position.
When the engine is running and the headlight switch is pulled the lights do pop up and go down when pushed in.
The hard part is trying to find the vacuum tank and actuators as they seem to be hidden.
It's a 1975, everything was working good until the car went to the mechanics and had the low beam headlights replaced for Australian conditions.
Now the headlight overide switch does not work and hisses when pulled down.
When the headlight switch is pulled out (with engine off) headlights do not pop up.
When the bypass switch is pulled down, headlights do not pop up and i can hear hissing coming from the switch. The switch looks new, as do the hoses and both switch and hoses are colour coded and are in correct position.
When the engine is running and the headlight switch is pulled the lights do pop up and go down when pushed in.
The hard part is trying to find the vacuum tank and actuators as they seem to be hidden.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Sounds like the headlight switch is operating normally.
So both the HL switch and the pulldown are working normally with the engine on ?
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Go to this link,scan down to 73-79 and it will show the vacuum tank is just behind the front bumper.
http://willcoxcorvette.com/instructi...ted_080509.pdf
http://willcoxcorvette.com/instructi...ted_080509.pdf
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
This little guy in this link might be your problem.
http://willcoxcorvette.com/product_i...oducts_id=5812
http://willcoxcorvette.com/product_i...oducts_id=5812
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
If you would like to see if the check valve is your problem,start the engine,pinch the hose between the check valve and manifold,turn engine off(keep pinching the hose)listen for hissing,wait 15 seconds and release pinch,if you hear hissing replace check valve.
Thread Starter
Instructor
Joined: Oct 2010
Posts: 140
Likes: 0
From: Sunshine Coast Queensland Australia
Thanks Roger, I see that the tank is part of the front structure.
How do i test the check valve?
I wont get a chance to look at the car until the weekend and will be looking for a disconnected hose or bad valve.
At least in the short term headlights do pop up when engine is running.
Chris
How do i test the check valve?
I wont get a chance to look at the car until the weekend and will be looking for a disconnected hose or bad valve.
At least in the short term headlights do pop up when engine is running.
Chris
Racer
Joined: Feb 2007
Posts: 271
Likes: 25
From: Buena Vista Colorado
How do i test the check valve?
1. Pull the check valve out of the car.
2. Hold the valve so you are looking at the side with the single port (the port connected to your intake manifold).
3. Put that port to your lips and try to blow through the valve.
4. If you CAN blow through the valve, it is BAD (allows atmospheric pressure into your vacuum system).
Burning Brakes
Joined: Dec 2008
Posts: 971
Likes: 45
From: Middlesex NJ
If he hears hissing at the bypass valve when he is operating it, I would think that either the bypass is broken or the hose came off and when he puts it in bypass its simply sucking air?
Hissing at the bypass indicates that vacuum is present and its just not being contained when the switch is operated?
Hissing at the bypass indicates that vacuum is present and its just not being contained when the switch is operated?
Le Mans Master
Joined: May 1999
Posts: 6,692
Likes: 29
From: Texas
The headlights will only go up with the car on. If you shut the car off with the headlights still up, they will stay up and until you re-start the car. You should not hear a hiss at all under the dash whether the switch is pulled or not. I am thinking you have a hose that was knocked loose under the dash or right inside the engine compartment. look at the bypass switch real close, it may have a crack in it.