Peteysquat

I have a 1971 vette and the headlight doors and wiper cowl door used to work fine. Now, neither of them open up. All vacuum hoses are hooked up and i don;t see any cracks/leaks in them. Engine runs fine. Any thoughts on what/how to check for the culprit? Thanks!

Peteysquat

tomdoc

Hi Petey. I am in the process going thru this myself. The best thing you can do is wrap your head around the understanding how both the wiper door and headlight systems operate. I spent 20 or 30 minutes this week doing just that. Many good posts on this subject on the forum. Also buy yourself "Troubleshooting The 1968-1982 Corvette Headlight and Wiper Door Vacuum Systems" from Zip or Paragon. It is priceless to have in your library for these cars. Also Wilcox has a very easy to understand schematic. Good luck, Tom.

Peteysquat

Hi Alan,

Thanks. Yes, I have checked the hose connections and worked the switches multiple times but this doesn't seem to make any difference.

Peteysquat

Hi Tom,

Thanks for the leads. I'll check them out. If by chance you come across some enlightening discoveries much appreciated if you pass them along! Thanks and good luck to you also!

Petey

tomdoc

Hi Petey, This morning I traced and found the problem with my windshield wiper door always being open. It was the vac hose from the override switch under the dash to the actuator relay. It was super easy to diagnos, find and fix because of studying the wiper and light vacuum schematics !! Once you wrap your head around the way these systems work it's actually enjoyable finding the problem!! I have been asking so many questions here on the forum but untill I looked at the schematics and diagrams and finaly UNDERSTOOD how these systems operate nothing made sense. I highly, highly recomend you buy the operations manual I mentioned above !! Good luck, Tom.

0Willcox Corvette

Tomdoc is exactly correct.. you have to get the system in your head first. You must realize that the system by default is to open and that it takes vacuum on the small hoses to keep the doors closed. Without vacuum on the small hoses the relay plunger drops and vacuum pulls the door open.

Go to the relay.. either the headlamp relay or the wiper door relay and remove the small hose... the door or headlamp housing should open up. It takes vacuum on these small hoses to make the item stay closed.

Then I would check the relays and see if I had vacuum on the yellow middle hose. This hose is what actually pulls the item open or closed.

If you don't have vacuum there then I would go to the vacuum tank under the inner fender and check it.

The vacuum system is not really that complicated and we have a video on how to test most of the items in the system. You just have to start in one area and test, then move forward.



1968-1982 Corvette Headlamp Vacuum Diagnostic Help.




69-72 Wiper Arm Vacuum Relay testing.

Peteysquat

Thanks for your help Tom! I have ordered the guide you recommended and look forward to working through the process!

Petey

ruken

I have one light door( the right looking from the seat) that works great. The left will not work at all. Replaced the headlight relay on the left side. The new one tested good. Hoses look good and vacuum test good with the mighty-vac. Do you have any idea what could be wrong? The hoses are run like the 73 model.

Rescue Rogers

When I had a leak I couldnt find I started at the engine vacuum and worked toward the split in the system. There is basically 4 vacuum sytems. 2 that act as the power to open and close and 2 that act as the switch to tell which system to open/ close.

I had a leaky wiper door actuator switch that bleed enough vaccum that my headlights openned real slow.


I disconnected the vacuum lines and used golf tees to close them and just followed the vacuum. Since its both systems you just need to split the system at the first tee after the filter and start there. The system tees again on the power side at the vaccum tank and on the switch side under the dash. One line goes to the headlight switch and the other to the solenoid.
Once you get one side to function you should have figured out what happened. Good luck. Keep us posted

old city

Thanks WILLCOX CORVETTE for that post. Will be useful to many.

ruken

I frogged(swapped) the three hoses on the headlight relay (good) with the three hoses on the other relay (bad) and now the bad one works perfectly(will open and close with the headlight switch) and the good one stays in the up(open) position. Is this telling me anything about what is bad. The small hose on the relay from the pull down switch stays the same.
ruken

Brcmpbl

Not looking to hijack here, but related question now that my memory has been nudged by this thread.

All the systems work properly on my 70 L46, but when I start the car the wiper door will momentarily open and then close again. That's all that happens. If I want to use the wipers, no problem - the door will open and close as it is supposed to. It's just the weird momentary open / close on start up.

This happen to anyone else? I haven't been able to diagnose it.

ruken

My 72 does not have the wiper door, it was removed and hoses run like a 1973. See previous post.


ruken

0Willcox Corvette

Your small hose side is loosing vacuum.

The default design of the system is to open the door when no vacuum is present on the small hose side. It was designed this way so that if there is a failure in the system you'll still have wipers. In this design the relay is designed to open the door when no vacuum is present on the small hose side.

So here is what is happening!
First keep in mind the larger hose will pull and build enough vacuum to function the actuator faster than the small hose side will build up to operate the relay.

When you start the car the vacuum isn't present on the small hose (but building up) and the door starts to open.
Once vacuum builds up in the small hose side the relay switched to the pull down position and the door closes.

Now the challenge is to find the leak.

It could be any one of the items from the tach solenoid, the over-ride switch, the wiper arm switch or a crack in any of the associated hoses.

The most likely culprit is the wiper arm switch. If you have already replaced this with one that is imported I'd bet the house this is your issue.

US Made correct working switch can be found here: https://willcoxcorvette.com/corvette...t-really-works

-Willcox

Brcmpbl

Thanks Willcox - that makes sense, because if the car is turned off for only a short time and then turned back on, the door only moves a tiny bit before closing again. If it sits a long time, it does the full open and then close.

I'll test the wiper arm switch.

0Willcox Corvette

Use this video to test it.. it is correct. There is one floating around on the tube that'll have you testing from the wrong port.