Headlight gremlins 70s c3

[Old guy]

Hey, dash pulled (long story why), and re-installed. Every gauge and wipers, headlights worked as they should prior to dash out and now in. Now it's a LHD car and when the car's started the headlights pop up. When engine off they stay up. I manually push them closed. Rinse and repeat...same same each time. Sure there's 500 things it could be and I've spent hours reading US web sites and have amassed a pile of maybes which I'll attempt soon (maybe not ).

However, my only question is this:- just behind the pull on/off switch on the LHS of the instrument panel is a plastic bit with 2 prongs on it for the vacuum hoses to attach. If they are on back to front, will what I'm experiencing be the cause? I'm asking here first before I again pull the dash. That way if it is this fault I don't need to go hunting through 50 feet of hoses, solenoids, etc ,etc. and remove the centre console bits too. I can go straight to this area.

[Vettech]

I'm sure Sirfixalot will have the ideas on this, my C3 knowledge is old. But!

If that happens it say's to me that upon start the Vacuum rises, goes straight to open mode and up they come.
So it may indicate swaped vac lines, I'm off looking in my book to refresh my memory.

The vac lines are colour coded.

Two lines thru fire wall, 1 black, 1 white which goes to a plug that goes onto the Manual Overide valve, whilst the black goes straight to the Light Switch. Plus a short blue line goes from Light Switch to that plug on the manual valve.
Once you pull that valve down it overides the headlight switch and allows the HL's to pop up without the lights actually being on.
Of course these colours are original for 78, but over time they may all now be black replacements.

The colour is a stripe. Maybe ill get this pic to stick.


 

[Old guy]

Cheers. I'm thinking they're back to front. I recall I didn't take particular note of the way they went when re-installing (my brain was fried after spending a zillion hours refitting everything). Speedo/tacho need to be dropped to access this I assume? Partial drop from the top I hope?

[Vettech]

You should be able to reach under to that over ride valve to operate it.

[Old guy]

I can access those 2 hoses attached to the switch and reposition them by squeezing my hand under the dash? Is that what you're saying?

[Vettech]

That over ride valve should be reasonably accessable as far as the pull valve is concerned, in my 78 all i do is reach under and its virtually at my finger tips - pull it and wahla. It would be more difficult to get your hands on the light switch (hoses).

Also my 78 is RHD, but the pic is for original LHD 78 build book.

[Old guy]

I'm not talking about pulling the over-ride switch, I'm wanting to re-arrange the 2 hoses that slide onto the part behind the pull on/off switch which is up high to the left of the speedo.

[Vettech]

Ok. Yes for that it is an issue,  when I did what your doing I had seat out and its slide in upside down head first under the dash, and for  a 6ft 1" gumby like me its difficult.

[Old guy]

Bummer. I was hoping I could just drop the speedo/tacho panel down a bit (without completely removing it), and get my hands up into it and switch the 2 hoses around. I hate this car and its wiring!!!! 

[Vettech]

I'm not sure that is the problem. The black line is Vac from the reservoir, goes into Light Switch, when pulled the vac is supplied to the short blue line to the over ride valve, which if in normal position allowes vac to flow into the white line, thence forward to the Vac Relays up front near the H'light assy, thence H'lights open.

All the up front H'light gear is supplied with its own source of Vac straight out of the steel reservoir that is part of the frame etc.

Ergo once up they stay up, unless the relays controll vac is interupted (white), ie light switch pushed off - but if the over ride valve is pulled then the white return line is sealed off and the relays will hold up.

And if due to age and leakage they do eventually drop, then the question is HOW do they come back up, upon restart as the H'light switch is off and the over ride valve is ...... um sorry to say it but, I'd be inclined to remove and test H'light Switch unless Sirfixalot has a better suggestion. He might be in Covid Lockdown on the beach.

I think also the relay's control line (white) must be vented to atmosphere not just closed off. Sorry my mind is winding back.
The front HL control relays have four (4) hoses, also HL up/down actuators have two (2) and once up they stay up and require the supply to be swapped over to drive closed.
The relays top most hose is white drives the internal bellows up/down. (White control line from H'light switch)
The next hose goes to actuator
The centre hose goes to main Vac source.
The bottom hose goes to actuator.    Thus the relay is a change over style and supplies vac to one side of actuator and atmosphere to the other, bingo it drives H'light open - upon relay de-activating, it swaps the feeds so the actuator closes the H'light.

Its the 14.7psi of atmosphere they rely on to supply the brute force to open the weight of H'light and lock. Time for Bourbon.

[Vettech]

Well ! Mr. Old Guy, please let us know what you found.

[Old guy]

Hi, haven't had the energy to look at it as it's again going to be a mammoth task (hence I was hoping hugely I could just switch those 2 hoses around). Now I'm in a normal 2 car garage (came from a 3 bay machinery shed), where there's stuff all room and I'm not sure where to start, apart from tearing down the dash....again. 

I might wait till I can get a mechanic to do a smoke test firstly. Maybe he has some ideas too, as he's worked on old vettes before. Other than his ideas, I may have to pull it apart. I'll let you know what I find 

[sirfixalot]

If you swap the hose on t fitting and hose on top side of over ride switch under dash you will effectively reverse the hoses at the headlight switch without having to remove headlight switch and dash. Normally if hoses are reversed at headlight switch you can hear vacuum leaking to atmosphere.  Both hoses should be readily accessible under dash if you take out lower vent duct