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Hello, My friends 68 Corvette has a headlight switch issue. When you pull the headlight switch the bulbs light up but the doors won't open. I replaced the headlight switch but didn't solve the problem. When you pull the service switch below the steering column, the doors open fine. The wipers and wiper door functions perfectly. The car runs great so there doesn't appear to be a vacuum issue.. Any thoughts? Thanks,, Jim
PS: the car has no A/C.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
Take the old headlight switch and test the vacuum ports and make sure it was bad. If it was not then theres a very good chance you have some hoses in the wrong location. IT doesnt mean that you didnt hook them wrong after the install but its a good indicator that it would be the 2 on the switch. If pulling the override makes them go up then everything from the override forward is connected correctly and functioning correctly. it could be that hoses 7 and 8 are switched because you have vacuum at the override. The override vents the line so the headlights pen. THen when you close the override, vacuum is applied and it pulls the relay valve back which changes the vac signal and you get vacuum on the other side of the actuator...theres always the chance that you got a bad headlight switch new out of the box....seen that a lot lately with the actuators
could be 7 and 11 are switched as well....trace the lines under the dash and you should find a solution
Last edited by Rescue Rogers; Aug 3, 2021 at 05:47 AM.
First of all... Thanks for serving our great country! I really appreciate the schematic and the information. I'm very disappointed that while I had the new switch installed and still exposed, I didn't reverse the two vacuum lines on the switch. Is there only one correct way to plug the vacuum lines on the switch? Also, is there a way to test the old switch please? I'll try and follow the schematic to see if any line is connected wrong.
Is there a way of testing if the two lines are reversed without getting to the switch itself? Absolutely. 1 - Pull the small control vacuum hose off the check valve. Hook up a vacuum pump to it.
2 - Block the vacuum hose after the "T" connection going to the solenoid behind the tachometer. This can be done by squeezing the hose with a vice grip type tool or putting a "golf tee" into the hose end. (If the wiper door circuit is holding vacuum this isn't really necessary, but it eliminates any question about it's condition).
3 - Squeeze closed the control vacuum hose going to the front headlight relays, (again optional, but will save you some pumping).
4 - With the over ride closed, and the headlight switch off, you should be able to pump up the headlight switch circuit and it should hold vacuum. With the h/l switch off, it just transfers vacuum through it. It's when the h/l switch is pull out to the on position that a reversed hose scenario will show itself.
5 - With the h/l switch on, if the vacuum reading goes immediately to zero, the hoses are reversed. Reason is the forward port is designed to allow atmosphere into the circuit now. If vacuum is retained, the hoses are properly routed. Reason is the rear port is designed to block vacuum upstream on the control circuit to prevent a vacuum leak.
This testing procedure mirrors the actual operation of the system, allowing testing of the headlight switch without pulling it out, which can be a real pain as we know. Bottom line, vacuum source hose to the port closest the the pull ****. In line vacuum hose going to the over ride connects to the port farthest from the pull ****.
Last edited by Plasticexperience; Aug 4, 2021 at 03:28 AM.
“If your not worried about the color coding of the lines, you could climb under the dash and switch the HL lines at the other end ie... The pull down blue stripe, and tee line white stripe to confirm lines are switched after following Dave's outline above. Control line has white skunk stripe and if installed correctly comes in from the fire wall off the check valve small port. It then tee's off to the HL port and attaches to solenoid valve on rear of tach. Rear of tach line has a yellow stripe but still same circuit. The rest of the lines to the pull down are blue stripe coded.” Marshal
Last edited by Plasticexperience; Aug 4, 2021 at 03:22 AM.
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help! 68 headlight doors won't open with switch
