I have a 69 coupe and when I turn the headlights on I get a hissing sound coming from under the dash. I have read the vacuum lines could be mounted backwards on the switch. What is the best way to access the back of the switch to check the connection? Can it be done without removing the dash? The headlights operate normally

Also when I turn on headlights the headlight warning light stays illuminated. The light does not illuminate when using the override switch. Do I have a bad cutoff switch? How do I test them?

Thank you

 

My guess is that your rubber lines have had it.

You will need to crawl around under the dash and check your lines. After 45 years the lines have probably cracked.

 

My headlight switch leaks vac when I turn the light on...got a new switch but haven't put it on yet. I have taken it, the dash panel, lose on the side and across the top and pulled the corner down to access it before. Its a job I don't look forward to...lol
It's at least one pack of cheese crackers and coke job...2 packs of crackers on a bad day!!

 

The lines look to be new. Just need easiest access to headlight switch.

 

You may try reversing the lines on the switch first. I have heard some of the service manuals have the diagram backward.

 

I replaced the headlight switch and control hoses in my 70 about 6 month's ago. I thought it was rather easy... below is a write up I did last week for someone else.

Disconnect the battery.

Removed A/C duct from under dash. Mine just slide out but I believe there is supposed to be a screw holding it in. I don't know what's under a non A/C cars dash, but I assume it's simpler.

Remove the drivers side kick panel (couple of screws).

Drop the steering column by removing the two bolts under the dash pad. This will allow the steering column to lower about 2".

Remove all the dash pad screws, this allows the dash pad to slide out and down to gain access to the headlight switch. Be careful with the dash pad as it's brittle and will break easy. If you need more room you could remove the steering column bolts at the firewall and gain a little more room, I didn't have to do this.

At this point you should be able to reach in and unplug the electrical connection and vacuum hoses. Pay attention to which hose goes where.

Now you can remove the headlight switch. First you remove the headlight switch ****, and there is a trick to it. Pull the headlight **** to the full ON position. Reach under the switch in front of the vacuum hoses and there is a small spring loaded button. Push the button in and you can pull the **** the rest of the way out.

After the **** is removed you will see a big retainer nut that can be removed with a large flat blade screw driver. I actually didn't have a screwdriver big enough so I used some small needle nose pliers. Once the retainer nut is removed the headlight switch will slide out.

I also replaced my vacuum control lines at the same time. I broke off a golf tee and plugged the new line into the old line. I than reached under the dash and pulled the new line through using the old line.

I replaced the headlight switch and vacuum hoses in about an hour and I'd never done it before.

 

Thank you, a few questions: you are accessing the switch from the top, correct? Why the need to remove the AC duct which is below the switch. Mine is a non AC car but I have the Astro ventilation duct. Regarding the dash pad, are the screws just on the outer left and right edge? I read somewhere there is a screw underneath that attached it to the firewall.

 

As far as the headlamp warning light is concerned each headlight door has a readily available inexpensive switch. They have often fail over time. They are accessible from under the car and are probably one of the easiest fixes there is on these cars.

 

Check out this thread;

https://www.corvetteforum.com/forums...-question.html

You can test the vacuum hose routing easily. If indeed the hoses are reversed, crawl up under the dash and reverse the hoses at the OTHER end. Remember, the vacuum supply hose goes to the switch port closest to the pull ****. Also, some brief hissing could be attributed to the fact the h/l switch allows atmosphere into the downstream circuit to allow the h/l's to open. If they are opened with the over ride, atmosphere is allowed into the system at a different point (over ride).

 

I wrote that all up from memory last week, I replaced the switch 6 month's ago so I could be forgetting something, but I know I hit all the highlights.

I did just go out and look at my car and remembered I had to remove the door sill plate (4) screws to remove the kick panel. I also had to remove the small molding under the steering column (3) screws to allow the dash pad to slide down.

The dash pad has (3) screws across the top. (2) screws on the right, accessed from the radio side, and (2) screws on the left, accessed from the door jam. The screws in the door jam required a stubby screw driver. All dash pad screws can be removed while sitting in the drivers seat.

The AC duct came off so I could replace the vacuum hoses, I can't think of a reason it would need to come off for just the switch. I also could have removed the duct at first when I tried to access the switch from below and behind. That was a no-go.

 

So are you accessing the switch from above or below/underneath the dash?

 

Yes, from the top. Actually from the top left hand side of the dash pad.

After you drop the steering column and slide the dash pad out and down you have about two or three inches of room to reach behind the dash pad.

 

There is no free lunch. You'll have to loosen the dash pad and lower the steering column to the point where you can get to the light switch.

Where do you hear the leak? "Under the dash" is likely to be the over ride and not the switch. "Behind the dash" is probably the switch.

 

Hi BH,
Yes.
You can access the switch's hoses from the top.
Reversed hoses can cause the hiss you're hearing.
Regards,
Alan

Blue striped hose forward nipple.


Blue striped hose at the vacuum over-ride pull switch.

 

It is possible to remove the headlight switch without lowering the steering column. I've had mine in and out a couple of times on my 73 for various reasons. First, disconnect the battery! Then, remove the headlight switch ****, the process was mentioned above. Next, I just removed the top three dash pad screws, the guage cluster screws for that side, the two in the door jamb, unscrewed the black air vent pull, removed the kick panel, removed the screws holding the vacuum bypass to the lower dash, and finally I removed the three screws holding the vinyl access plate on the steering column. Then proceed with caution as you gently pull on the left corner of the dash pad. You should be able to access the switch and the hoses at this time. Note, it is a tight squeeze in there but it can be done.
Good luck,
Jim

 

Lowering the steering column is a two minute job as it's only two bolts and will give you an extra inch or more of room. You just remove the two bolts next to the vacuum override switch. The extra room can be really helpful to some so they don't put pressure on the dash pad and break it. Those old dash pads can be really brittle.

 

Hi,
Don't forget the 2 screws from the side of the center gauge cluster.
Also, at least on my 71, the bracket that mounts the parking brake bracket to the hinge pillar needs to be loosened too in order for the dash pad to drop down far enough to get your fingers to the hoses.
Regards,
Alan

A lot going on under that corner.

 

Thanks Alan. I am going to work on it this evening. I also have a turn signal indicator light that needs replacing so thinking of taking care of that as well while I have the dash apart. When you say parking brake do you mean hood release? my parking brake is in the center arm rest.

 

Hi bh,
Yes!
Brain exploded!
HOOD LATCH release bracket!!!!!
Regards,
Alan

 

I didn't have to do this on my 70. It would be interesting to know why they are different. Perhaps the difference between AC and non AC?