I've searched the forum for this problem and could find one that was close, but the resolution to that one is not a resolution for mine. I have 78 Vette. I have vacuum checked 80% of the hoses and they hold vacuum, both of the actuators have been vacuum checked and open and close with my vacuum hand pump and their hoses. I have NOT checked the control units, but they are new (I know the kiss of death). The light switch and the vacuum release switches are brand new as well. I've checked all the hoses and they are all connected over the entire system.

Here's what happening. When I turn on the lights, they don't open (I've waited a couple mins to even see some movement - none). If I open the release switch, the right light pops up and the left one slowly opens after a min or two. I can turn off the light switch but the lights didn't go down until I closed the release switch - I haven't tried closing the release switch first and then the light switch (last night was the first time they went down by themselves).

One more caveat, I have hooker side manifold and side pipes on the car and I'm not sure that hasn't had some effect on the vacuum out put. Anyone know the reading the output should be at the manifold? FYI I had problems with the lights before I put the side pipes on.

Any thoughts?



|UPDATED|7/17/2017 7:01:20 AM (AZT)|/UPDATED|

Could the header install partially melted a vacuum line?

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1973 L-82 4 spd

Thanks for the response. No the out port for the vacuum is located on the Intake Manifold on top of the engine.

Do you have vacuum at the headlight switch itself?

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1973 L-82 4 spd

I would assume so, I've never ran the engine and put the gauge on it, but I have vacuum checked all the lines in between the output port and the headlight switch, including the spliter and filter. Since the lights react to the release switch and the release switch gets it's vacuum from the headlight switch and having vacuum is necessary for the switch to open and close the lights, I'm pretty confident it does. Thanks for the suggest though.

Have you measured how long the vacuum reservoir holds
 the vacuum after you shut the engine off?

How much vacuum does the engine produce at idle?


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1973 L-82 4 spd

Milt, I sent you some vacuum troubleshooting info via e-mail....it should be able to help fix the issue. 

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Joel Adams
C3VR Lifetime Member #56    
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