Winking headlight...still...next steps?
Thread Starter
Cruising
Joined: Jul 2019
Posts: 13
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Winking headlight...still...next steps?
Passenger side would come up very slowly...and not come down without a manual release.
We enlisted our favorite mechanic..
All of the hoses appear to have been replaced by the prior owner and look to be in very good shape, our mechanic didn't find any vacuum leaks.
He checked and the vacuum system test pointed to the actuator being bad, we replaced it today and it does come up much faster, but still will not go down.
Coincidence or another step in diagnostics..now the driver's side comes up slower than it had before, but will still go down.
We tried swapping the hoses to test the relay, from driver relay to passenger actuator...it came up slow..and wouldn't go down, we ran out of time to swap them in reverse to check if possible mechanical vs vacuum issue (that's tomorrow's game plan).
We also noticed that we don't have a vacuum filter in line behind the vacuum hose check valve...we saw mixed comments on if we should add it back.
Also conflicting advice (oldest comment several years ago), whether a failing check valve would cause this issue.
Any suggested next steps would be greatly appreciated.
We enlisted our favorite mechanic..
All of the hoses appear to have been replaced by the prior owner and look to be in very good shape, our mechanic didn't find any vacuum leaks.
He checked and the vacuum system test pointed to the actuator being bad, we replaced it today and it does come up much faster, but still will not go down.
Coincidence or another step in diagnostics..now the driver's side comes up slower than it had before, but will still go down.
We tried swapping the hoses to test the relay, from driver relay to passenger actuator...it came up slow..and wouldn't go down, we ran out of time to swap them in reverse to check if possible mechanical vs vacuum issue (that's tomorrow's game plan).
We also noticed that we don't have a vacuum filter in line behind the vacuum hose check valve...we saw mixed comments on if we should add it back.
Also conflicting advice (oldest comment several years ago), whether a failing check valve would cause this issue.
Any suggested next steps would be greatly appreciated.
Drifting
Joined: Nov 2013
Posts: 1,547
Likes: 282
From: Scottsdale Arizona
I had a similar problem with my 77. The passenger side headlight would come up on acceleration and slowly go back down when I let off the gas. It turned out that the vacuum hoses were reversed on the headlight switch.
Le Mans Master
Joined: Aug 2006
Posts: 7,427
Likes: 1,560
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Hi and welcome!
You may have a bad relay but test each part before you order more parts.
Heres how:
http://www.corvette-101.com/vacuum.htm
Heres how:
http://www.corvette-101.com/vacuum.htm
Burning Brakes
Joined: Jul 2018
Posts: 979
Likes: 258
From: Maryland
You can check each headlight unit separately for up/down operation using a mighty vac (I got mine from Harbor Freight).
1. To make the headlights go up, put the mighty vac on the GREEN striped line into the actuator. Now put some vacuum with the mighty vac on the GREEN striped line. It will take a bit of doing, but the headlight should slowly rise.
2. To make the headlights go down put the green line back, and then put the mighty vac on the RED line into the actuator. Now put some vac with the might vac on this line and you should see the headlight slowly go back down.
If these tests work, your actuator is probably doing it's job. On some of the later C3 models, there is one relay valve for each headlight actuator. (My 69 only has 1). The vacuum comes in on the YELLOW line and is switched to either the
GREEN (up) or RED(down) lines depending on the state of the small white control line.
1. To make the headlights go up, put the mighty vac on the GREEN striped line into the actuator. Now put some vacuum with the mighty vac on the GREEN striped line. It will take a bit of doing, but the headlight should slowly rise.
2. To make the headlights go down put the green line back, and then put the mighty vac on the RED line into the actuator. Now put some vac with the might vac on this line and you should see the headlight slowly go back down.
If these tests work, your actuator is probably doing it's job. On some of the later C3 models, there is one relay valve for each headlight actuator. (My 69 only has 1). The vacuum comes in on the YELLOW line and is switched to either the
GREEN (up) or RED(down) lines depending on the state of the small white control line.
Thread Starter
Cruising
Joined: Jul 2019
Posts: 13
Likes: 0
Thank you Peterbuilt and jpatrick62, we pulled each line, verified what our mechanic told us..the lines are intact...hold pressure no problem.
We did find the following problems: The Vacuum check valve failed the vacuum test..but not the cause of our currently identified problem...but it is on the list of fixes..
Vacuum filter..we don't have one, also on the to do list
Head Lamp Relay Valves...yep..they both failed the vacuum test miserably....
the only step that passed was the valve movement. #1 and #4 on the list were both unable to maintain vacuum...no filter on the bottom of either to prevent crud from getting inside, not too shocked since they appear to be original.
We stopped there...new Relay Valves on order..if we need to go further down the check list..we'll try that next.
We did find the following problems: The Vacuum check valve failed the vacuum test..but not the cause of our currently identified problem...but it is on the list of fixes..
Vacuum filter..we don't have one, also on the to do list
Head Lamp Relay Valves...yep..they both failed the vacuum test miserably....
the only step that passed was the valve movement. #1 and #4 on the list were both unable to maintain vacuum...no filter on the bottom of either to prevent crud from getting inside, not too shocked since they appear to be original.
We stopped there...new Relay Valves on order..if we need to go further down the check list..we'll try that next.
