Topic: Headlight Vacuum Help
in Forum: C3 Body
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I need some help with the headlight vacuum system on my '74 please. To bring you all up to date on this problem, I recently replaced every component in the entire headlight vacuum system including hoses, relays, actuators, filter, check valve, headlight switch & override switch.
My problem is the headlights pop up as soon as the engine is started whether the headlight switch is on or not and they will not go down. If I reverse the Green & Red hoses going into the relays the lights will close and stay closed until hoses are returned to their proper position on the relays.
Joel was very helpful and sent me a copy of the troubleshooting guide. I have tested every component and everything tests good. I have checked all the hoses for leaks and all check good. My vacuum tank has no leaks and holds a vacuum. I have retraced all hose connections and all are correct. Anyone else have any problems like this or have any clue what I’m missing?
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Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Dadgum....I know you've been fighting this for a while....
I gotta ask the dumb questions, so don't get mad....
Are you sure the over-ride switch is in the proper position? Will the over ride switch move the lights at all?
If you LEAVE the hoses reversed on the relays, will they work properly with the headlight switch then?
Do you hear ANY air leaking from the headlight switch at any time?
Will Lassie get Timmie out of the well in time for supper?
If you remove the check valve form the system, will the lights work properly?
If you reverse the hoses on the actuators(the large cans), do the lights work properly?
It's strange that you have all these new parts, and still have this problem. Normally lights that flop up when you start the engine have only a few things that cause that....bad relays, bad check valve, or bad headlight switch. I do know of a certain person who shall remain nameless that has called me more than once with this issue....only to find he had pulled the over ride switch down un-knowingly....
I gotta ask the dumb questions, so don't get mad....
Are you sure the over-ride switch is in the proper position? Will the over ride switch move the lights at all?
If you LEAVE the hoses reversed on the relays, will they work properly with the headlight switch then?
Do you hear ANY air leaking from the headlight switch at any time?
Will Lassie get Timmie out of the well in time for supper?
If you remove the check valve form the system, will the lights work properly?
If you reverse the hoses on the actuators(the large cans), do the lights work properly?
It's strange that you have all these new parts, and still have this problem. Normally lights that flop up when you start the engine have only a few things that cause that....bad relays, bad check valve, or bad headlight switch. I do know of a certain person who shall remain nameless that has called me more than once with this issue....only to find he had pulled the over ride switch down un-knowingly....
Joel Adams
C3VR Lifetime Member #56 
My Link 
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Gary, I thought about that Saturday night so Sunday morning I tore the dash out (again) to check.. They were in the correct position.. Thanks
Joel,
To answer all you questions in order, and no way am I mad, I need all the help and double/triple checking I can get...
YES, NO, NO, ....
Are you sure the over-ride switch is in the proper position? YES
Will the over ride switch move the lights at all? NO
If you LEAVE the hoses reversed on the relays, will they work properly with the headlight switch then? NODo you hear ANY air leaking from the headlight switch at any time? That's a tuff one cuz I'm about 75% deaf so I can't hear any airleak that small.. I will have my wife come out & lend an ear..
Will Lassie get Timmie out of the well in time for supper? Hope so, June is a good cook!
If you remove the check valve form the system, will the lights work properly? Have not tried that.. tested good but will pull it and see if that works.
If you reverse the hoses on the actuators(the large cans), do the lights work properly? Have not tried that but did test them according to your trouble shooting guide and they tested good. Will try it too.
I'm a long haul truck driver and on the road right now, I'll try all these suggestions next Saturday when I get home again.
Thanks again for you help
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
The actuators should have vacuum on them in the DOWN position with the engine running. If the lights are coming up when you start the engine, then obviously the vacuum is going to the wrong side. If it was just that, then they should go DOWN when you turn the headlight switch on.There is a problem with the control of the vacuum, and it effects BOTH sides. It has to be either the headlight switch, or the relays....I'll try to find a little more diagnostic info....
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
some diagrams have the override sw vacuum lines wrong. Blue stripe should be closet to the knob, White should be at the top of the sw as it faces down. it is in the off (no override, lights Closed) when pushed up it is pulled down to open lights
|UPDATED|11/5/2013 1:35:25 PM (AZT)|/UPDATED|
|UPDATED|11/5/2013 1:35:25 PM (AZT)|/UPDATED|
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
I have also heard that, Bob.
See if THIS digram helps. I don't think I sent this one to you....just disregard the yellow stuff going to the wiper door....the rest of the system is the same, tho.
See if THIS digram helps. I don't think I sent this one to you....just disregard the yellow stuff going to the wiper door....the rest of the system is the same, tho.
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Many thanks to all that replied with suggestions! I think I found the main problem to be one of the hoses that goes to the bypass switch was trapped between the steering column and support bracket. I do believe that I also have a bad Light Switch and will replace that ASAP. The switch is leaking when pulled out but at least now the lights go up & down.
Thanks again.. this site is Great !
Where can I find vendor and information on converting the headlights to electric vs vacuum.
I'm planning front rivit repair and paint next year and that seems like a good time to do the conversion.
God Bless, rick
'75 Steel Blue Stingray Coupe
'75 Hot Red L82 Stingray Convertible
in Forum: C3 Body
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