On my 73 I have replaced the headlight actuators, vac valves, check valve and filter, headlight switch, underdash valve and all the rubber lines. I believe that's about everything in the system. I didn't change these parts chasing a problem but in the course of restoring the car.

I tried to be extra vigilant when assembling this thing as far as proper hose connections.

My headlights now will only go up when I pull the underdash valve out.
I have double checked all the hose routing and connections except the headlight switch.

I did note that the headlight switch I put in felt stiff and kind of extra notchy when pulled it out the first time then felt ok after that.

I am wondering if something might have been off in the vacuum switch portion of that headlight switch that would cause the extension issue?

I have yet to confirm the proper hose connections on the switch because I'm putting off removing the dash pad, but I guess I'm going there next.

I am tempted to spend another $32 for another switch and try it when I take the dash pad off. Anybody had a similar issue?

Thanks in advance
Mark

 

Yes , when I finished working on the dash gauges and had the whole dash put back together I had the same problem (from Memory) instead of pulling the dash I just swapped the hoses at the first connection , I think I had to cut one and add some hose as well to join in with the other but no way was I going to pull that down again . Worked a treat !

I have had switches that were hard to use first time and they were ok after as well so you might be ok there ,hopefully !

Good luck

 

I'd hold off on the switch and just verify the hoses on the switch. There have been may vacuum diagrams posted over the years that have the hoses reversed... This was caused by someones personal OCD obsessed vendetta against another vendor...

So how do you verify the headlamp switch connection.. easy.

If you use the diagram below... pull the vacuum hose off the over-ride switch D.. it takes vacuum to hold the lamps down not up. The system by default, if vacuum is lost will open the doors.

So you want to check the blue stripped hose H and see if there is vacuum on it with the switch off.. If there is vacuum, then pull the headlamp switch on and see if the vacuum is blocked. The headlamp switch should block vacuum on that blue stripped hose and if it doesn't then you either have the hoses reversed at the switch or you have a defective switch. If the vacuum is blocked on the blue stripe when you pull the switch on, then your issue is somewhere else.

While I don't advise customers to do this you can remove the two lower column bolts which will allow you to drop the column a little bit... The remove the three screws from above the dash pad and the two in the jamb and the screws from the center dash bezel to the dash pad... this will release the left pad. If you do this you can usually pull the pad back enough to check the hoses.

The issues.... be careful. Doing this will put the entire weight of the dash pad on the steering column and you can crack the U section of the ABS plastic sub straight. But it is do-able this way.

 

I think you are right, that the hoses on the switch may be reversed.

I would also check to see if hose H simply holds a vacuum when the switch is pulled.

If hose H holds a vacuum (even when it's not the engine vacuum) and the rest of the system does not have a leak, then the headlights will stay in whatever position they were in when the switch is pulled. Right?

 

Thanks, I'm on it, or soon will be. I am looking for a nice C5 now so I kind of got sidetracked, but I'll get to it soon.

 

I finally got around to the headlight issue. Got the dash pulled down just like you said, the vacuum lines were reversed, all is well now. Thanks much.

 

I thought I had my headlight retracting issues fixed thanks to advice about reversed vacuum hoses on the headlight switch. I had tried it several times and everything seemed fine. A buddy came over and I started the car so he could hear it.

When I shut the car off I noticed the headlights were up, I had never turned them on. I thought maybe the one of the hoses on the switch was leaking or had come loose, they are in a bit of a bind when the switch is installed.

So using the tip from Wilcox I dropped the left dash panel down and the hosed were connected and tight. As I was checking the hose fitment to the ports on the switch I noticed the plate with the hose ports was moving some. It is held to switch body by little metal arms that wrap around and are crimped over the plate.

I took the switch out retightened all the arms and the plate didn't t move then. Must have been a vacuum leak there so its all working as advertised again.

Long story short is when you install a new headlight switch make sure that port plate is tight against the switch body or you might have a issue like I did. It's much easier to tighten up that before you put the switch in.

 

I know this is a old post but, I'm working thru this right now if you are using the GM Service manual the drawing showing the switch implies the hoses are in reverse position. I was questioning this last nite

 

I did the same thing a few weeks ago - hooked the hoses up backwards. Headlights would not go down. Fixed it now - I'm getting pretty good at this!

 

I just checked, and you're onto something. My '70 service manual shows the vacuum source connected to the front of the headlight switch, but my AIM shows the vacuum source connected to the rear of the switch.

AIM:


Service Manual:

 

That's what I saw

 

The input is always the rear nipple on the switch for all cars 68-82.

And to compound things, years ago there was some bogus diagrams floating that one vendor did to mess with another vendor and what a nightmare that was. I've not looked at the service manual diagram in years because I drew my own that I know are correct.

All of the headlamp and wiper vacuum schematics are on the tech site and they can all be uploaded from 1968-1982 in this PDF. http://repairs.willcoxcorvette.com/w...schematics.pdf


Willcox

 

I mainly reference my AIM when working on my car. I was just surprised when the service manual had the hose routing drawn incorrectly.

 

I'm confused. Are you referring to the port closest to the **** as the rear? Your picture shows the vacuum to the port nearest the **** with a reference of vacuum to the rear? I would think of that as the front?

TIA Paul

 

Yes he is. That would be the port closest to the rear of the car.

Simple formula to follow; The source vacuum for the headlight switch AND the override switch always goes to the port closest to the pull ****. The reason is as follows;

Internal passages in the headlight and override switches are open, allowing vacuum to pass through the switches to the downstream component when the pull ***** are pushed in.

With the pull ****(s) pulled out, the source vacuum port blocks that port (closest to the pull ****). The farthest port from the pull **** is then open to atmosphere, effectively switching the relay internal piston.

 

 

Thanks for finding this thread and all the members who replied...I will be needing the info as I work my way to the front end of my project.

 

I replaced my switch several years ago. For the first little bit it felt stiff and notchy as the OP described. In fact it was stiff enough that the headlight switch rod would pull out of the switch sometimes. Then, suddenly, it felt normal. A little notch at the parking light position as it should. However the headlights did got move and I had to use the under dash valve. I bought another one but never installed it because it feels the same way leading me to believe there is a problem within the new switches. I finally did the switch to electric.

 

So Willcox should run a big sale on headlight system parts now.😜

 

Probably Friday or Saturday morning..