Headlights come on fine with switch but will only raise on lower with manual override? Would this mean headlight switch is bad?

 

Makes no sense...because IF your headlights stay down when you crank your engine...and the headlight switch is in the OFF position...and you can not hear any 'hissing' at the headlight switch ( which can be a problem)...then there is nothing wrong with the headlight switch.

This is because the vacuum is still going to the actuator relays via the small vacuum hose. The small hose on your relays is what is controlling the UP and DOWN function and it gets it commands from the headlight switch or override switch.

SO...with the engine running and the headlight switch off and the override switch pushed up...you should have vacuum on the small hose to your actuator relays.

When you pull the headlight switch or the override switch..the vacuum will stop....thus causing the headlight doors to go UP...when you add vacuum back onto the small vacuum hose...the headlgith doors go down...that is IF the hose routing is correct.

DUB

 

I checked the lines everything seems right. So here is the scenario I start the car turn on head light switch and lights come on but do not raise up until I pull the the manual override down then they come up fine.

 

Did you just buy this C3? If so the previous owner plumbed it wrong and was using the override to open and close them.

 

This is setting off warning bells. 'seems right' is an answer that makes me feel that there is still room for error and with this vacuum system...it HAS to be correct in order to work as designed. When checking the vacuum hoses and their routing the answer needs to be 'everything IS right'.

but the stated that he checked the routing of the hoses...

So...if you verified that the vacuum hoses are going to the headlight switch..which not knowing what year you have...some year models require dropping a portion of the dash in order to look in and see them....and IF they are correctly attached....then YES....the vacuum switch on the headlight switch can be bad.

Because if you have the vacuum routing diagram for the headlight system....then you know that the vacuum hose coming from the headlight switch that goes to the override switch. You could disconnect the connector at the override switch.....cap it off with your finger....crank the engine and then see if you feel vacuum on THAT line form the headlight switch. Then...pull the headlight switch and IF the vacuum is still present....then the problem CAN be in the portion of the headlight vacuum switch.

DUB

 

I chased all the tubing and it matches the diagram for a 68 vette. I have not taken the headlight switch out to make sure it hold vacuum. The windshield wiper door works fine with switch and override. Is it possible the solenoid is bad or the headlight switch?

 

If I may............
There is help on this forum that can do this in their sleep, like DUB.
You asked about head lights and then switched gears and asked about the wiper solenoid.
The solenoid is down stream so lets leave this one alone for now.
If the wiper switch and over ride activate and park the wiper system
you are better off than you realize.

Now lets tackle the headlights.
Vacuum comes in off a metal "T" nipple located behind the carb on the manifold. Then through a white filter, than a check valve, than onto the rear port of the head lamp switch. See Wilcox diagram for 68's.
Dave Jacobs who can write a book on this topic has a thread on this forum on how to test the head lamp switch in situ ie... in car.
No need to start ripping into the dash at this point.
If the switch fails its the switch, plain and simple.
If it passes, move down stream to the pull down on the left of the wiper over ride ****... 68 right?
If it fails the test then replace it.
The C-3 Vacuum system has 3 systems leap frogging off each other.
Wipers are linked into the head light system via a plastic "T" linked through the wiper solenoid.
HVAC system is linked off the main wiper relay supply line black hose yellow stripe via a very tiny plastic "T" in line nearer to the passenger side heater/AC box. These are brittle and do break. Doc Rebuild has them.

The threads for testing each component are here therefore I did not go over each testing method in this thread.
Isolate and rule out and you will find the culprit.
The head light system must be leak free first.
Next the wipers and lastly the HVAC.
If the headlights leak the other components go into default mode.
The wiper door remains open, the HVAC defaults to the floor heater mode by design.
I went through this over a year ago with my 68 coupe.
Good luck and let us know how you make out.
Report back as you trouble shoot each part of the system.
Do the head lights first!!! Or your just chasing your tail.
Marshal

 

I did not switch gears I’m just saying I traced all the vacuum lines and everything seems correct. I was just letting you know that the wiper door works fine and the headlights come up fine with the auxiliary switch but do not come up with the headlight switch. That’s why I’m asking if it could be the headlight switch. I definitely do not hear any leaks.

 

Its pretty simple...you have two line going to front on car for headlight actuators....if lightswitch doesnt cjange vacuum from one line to the other then switch is bad...no matter how you get them to go up, there is deffinately a problem with light switch...your probably lucky the bypass switch is still working...had it not been working then you would never no where to look, it only takes one little leak for nothing to work at all...

 

I have seen reversed vacuum lines at the headlight switch do some strange things. There are also a lot of vacuum schematics out there that are wrong about this connection.

There is a simple test to check the connection without taking the switch out or removing the dash.

1 - Disconnect the small vacuum hose at the check valve.
2 - Disconnect the vacuum hose at the metal port on the electrical connector side of the solenoid and plug it. You will find it at the bottom of the back of the tach. A small mirror helps here.
3 - Connect a Mityvac or equivalent pump to the small vacuum hose at the check valve.
4 - Pull the headlight **** all the way out.
5 - Pump up the vacuum hose. If it holds vacuum, you should have a proper hose connection. If no vacuum, the 2 hoses are probably reversed. When the **** is pulled all the way out, the closest port to the **** is designed to block incoming vacuum, and the farthest port is designed to vent (allow atmosphere in) the vacuum hose.

 

I knew Dave would be able to explain it in a few simple sentences.
Marshal

 

And if the hoses are switched at the headlight switch.,.,.you will hear vacuum 'hissing' when the **** is pulled out....or at least darn near every one that has been switched has hissed for me.

You have written this statement incorrectly.

You wrote:if light switch doesnt change vacuum from one line to the other then switch is bad.

SO this does not further confuse people who want to know....the light switch does not change the vacuum from one line to the other....the headlight switch is controlling the vacuum to the actuator relays. SO...IF you have vacuum on the small hose at your actuator relay...your headlights stay down....because the headlight switch is pushed IN.

When you pull your headlight switch or pull down on the override switch...this STOPS the vacuum to the actuator relay...and thus NO vacuum at the small hose at the actuator relays.....your headlight doors go UP.

The 'other' larger vacuum hose that goes to your actuator relays is the vacuum source that makes the actuators go up or down when requested. It is constant and always there as long as the engine is running and may still hold vacuum ii the system is sealed well for a short while after the engine has stopped ruining.

DUB

 

Excellent explanation DUB.
The relay vacuum operation at the small line reminds me of a train track switch for the rails.
The big lines are the source much like any power source.
The control side is independent of the source side and I remember having a huge mental block trying to understand the difference when I first learned about these systems.
They are actually brilliant and very advanced for 1968 in my opinion.
Marshal

 

It was quite ingenious and simple all at the same time. Once a person understands it.

And YES...it took me a little while for it to sink into my head a long time ago. Now it is second nature and I can find the problems in the system really fast due to understanding the principles of it.

The only tool I need ...if you even want to call it that.... is a hose or my stethoscope so I can listen for leaks in the actuator relays where they are know to leak vacuum. Diagnosing the rest of the system....for me..requires no tools. It is all done by hand. EXCEPT for me using my electric vacuum pump so I can verify a bad metal vacuum storage tank for the 1968-1972 vacuum storage where they are know to split and leak as like in the link below.

http://www.corvetteforum.com/forums/...nk-repair.html

DUB

 

Good catch dub...

 

I had a two year old switch break a couple of years ago. There was no vacuum leak that I could detect. I had to use the override to open and close the doors.

 

How to test the head light switch:
http://www.corvette-101.com/vacuum.htm#switch

How to hook up the hoses:

 

Just trying to keep the information correct due to this system often times can intimidate people.

100%...I have also encountered that.

The plastic and metal provision inside the switch can fail...and if the tab for the vacuum switch portion of the headlight switch is in the position that keeps the headlights DOWN...then you would not get a vacuum flow change and also not hear any hissing.

DUB

 

It definitely was a vacuum problem with headlight switch. Hooked up new one but the plunger won't stay in and I have no headlights now. They do come up and down with the new switch and I have running lights just no headlights.

 

I do not know what you mean by 'plunger'????

At your dimmer switch on the floor...you have to make sure that when you pull your headlight switch...I believe it is the yellow wire will get 12 volts on it.

DUB