Technical Tips > Electrical-Electronics-Air-Lighting-Guages-Security-Vacuum

Headlight gremlins 70s c3

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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!!!!  :banghead:

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.

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