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New to this thread, just purchased a 79. It came with a few issues, the main that I am dealing with is the headlights remain up and don’t even attempt to close when the lights are off. What I do know is that the owner before me removed the heater core due to a leak there, which from my research must have caused a vacuum leak? I found this hose that doesn’t appear to have a home, wondering if anyone has any idea where this goes or if it’s the cause of my issues. The car runs and drives just fine. Passenger side
Looks to be a heater core hose that would connect to the water pump just above the lower radiator hose.
You can cut it off where it's attached at the firewall.
RE: is your headlight override valve under the steering column pushed upward? The override is there if something happens that you need the lights up for some other reason without using the dash light switch.
Your car would only have one of the valves shown in this pic, the other was for the wiper door on earlier C3s.
Last edited by barkingrats; Jul 6, 2024 at 05:34 PM.
Looked at your engine pic again: appears they looped the upper and lower block connections for the heater hoses together with a single hose. Just remove what you have in your hand and toss it. That it's still connected to something, I suspect the previous owner didn't actually remove the heater core - merely took it out of the coolant loop.
Hey!
Thanks for the reply, I checked that valve under the steering column, it was pulled out. I pushed it back in and the headlights came down, however wont go back up.
The heater core hose has nothing to do with the vacuum system.
Glad to hear they went down when you pushed the valve up! Are you saying they won't go back up if the valve is pulled down again? (As 4-vettes said, your engine has to be running for the vacuum to be generated.)
Have you tried pulling the dash headlight **** out to turn the lights on? Do they stay down? Do you hear any hissing under/behind the dash?
Thats good to know, and yes the car is running when trying to get them up. A previous comment pointed out the override switch on the steering column and was able to get them down but now they wont come back up
I think it's time to hit the vacuum diagrams for the headlight system. Being that you have a '79 I'm not confident advising on routing from the front vacuum tank (earlier C3s had the tank under the left fender by the firewall). Here's the diagram I have saved, but it is for earlier C3s with wiper doors and the rearward vac tank – the few components on the left can be ignored for your car. Someone here will provide an appropriate diagram for your car.
Thank you for your help! Correct me if im wrong but the lights need vacuum to close as well right? So if they were able to close I shouldnt have a leak?
PS - you can still get the headlights up manually so you can drive at night. From underneath each headlight bucket there's a "knee" joint that if you press on it all the way until it's over-center it will raise and lock the door open. You can manually close the door by pulling that knee joint forward/down. Be careful of any wiring and the warning switch as it breaks easily.
Thank you for your help! Correct me if im wrong but the lights need vacuum to close as well right? So if they were able to close I shouldnt have a leak?
Yes, you need vacuum both ways. The headlight and under dash valve are small line hoses that go to controllers between the headlights (in the diagram the two centered components with all the hoses connected to them). These controllers move a small piston from one large hose to the other so that the main vacuum signal is switched, causing an open signal or a close signal to the actuators (the large pie-plate looking deals at the back of each door).
Do you have a Mity-Vac sort of hand vac pump? They're pretty handy to have to check these components.
I dont have a hand pump. In the morning I will have to go out and follow all of the lines and see if I can find anything obvious. I saw some use a flammable brake cleaner and spray the lines to try and locate a leak. Would it be likely to have 2 bad actuators? Confused as to why they were able to go down with ease but dont even try to come up
I recently had headlight issue that ended up being an actuator seal. But I had good vacuum and just one side wouldn’t go up. First thing I’d do is test vacuum with a vacuum gauge (cheap on Amazon) and test up and down the lines all the way to actuator relays/actuators. I believe I had something like 22hg vacuum, so knew it had to be actuator relay or actuator and did subsequent testing
I am surprised no one has mentioned what appears to be a plastic fuel filter in a rubber line with worm clamps over the exhaust manifold area in one of the pics.
I am surprised no one has mentioned what appears to be a plastic fuel filter in a rubber line with worm clamps over the exhaust manifold area in one of the pics.
Vacuum Leak
