1972 Manual Headlight Override Switch
08-09-2017, 07:55 AM
#21
Burning Brakes
I drove it yesterday for about 30 minutes. 15 minutes I had the override switch pulled. Nothing happened. 15 minutes I had the headlights on and nothing happened.
Last edited by LenWoodruff; 08-09-2017 at 07:56 AM.
08-09-2017, 08:45 AM
#22
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I would agree except nothing has been touched on the vacuum lines in many years and these were working a couple of weeks ago.
I tested the control line from those switches and there is vacuum when they are off and no vacuum when they are on.
The odd thing if the replays are the issue is that they both failed at the same time. I could see one failing but both is weird.
I tested the control line from those switches and there is vacuum when they are off and no vacuum when they are on.
The odd thing if the replays are the issue is that they both failed at the same time. I could see one failing but both is weird.
If the internal spool of the relay (relays) are leaking by the sealing surface it is possible that vacuum is then ported to the bottom of the relay. That is where the exhaust port of the relay valve is.
Last edited by bmotojoe; 08-09-2017 at 08:46 AM.
08-09-2017, 08:50 AM
#23
Burning Brakes
To be clear, you had vacuum on the small vacuum hose at the relays with switches off, and no vacuum at the relays with switches on?
If the internal spool of the relay (relays) are leaking by the sealing surface it is possible that vacuum is then ported to the bottom of the relay. That is where the exhaust port of the relay valve is.
If the internal spool of the relay (relays) are leaking by the sealing surface it is possible that vacuum is then ported to the bottom of the relay. That is where the exhaust port of the relay valve is.
Last edited by LenWoodruff; 08-09-2017 at 08:50 AM.
08-09-2017, 09:02 AM
#24
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Len,
1 relay may have been bad for a while and the 2nd one just quit.
Just a thought?
If a miti vac raises the doors then the actuators are still sound.
Relay is cheap get one or two and try it. Best to troubles shoot
both first.
Or as stated something under the dash is not plumbed right.
Marshal
1 relay may have been bad for a while and the 2nd one just quit.
Just a thought?
If a miti vac raises the doors then the actuators are still sound.
Relay is cheap get one or two and try it. Best to troubles shoot
both first.
Or as stated something under the dash is not plumbed right.
Marshal
08-09-2017, 09:40 AM
#25
Team Owner
You can test your headlamp vacuum system while only using your existing vehicle. Have car idling in the driveway/garage; pull the vacuum lines off of one of the headlamp relays and determine which has vacuum on it; connect that hose to the center fitting on the relay (that is vacuum SUPPLY). Do the same for the other relay.
Note: If there is little or no vacuum on these lines, there is a problem with the vacuum supply system.
With the supply lines hooked up to the relays...and the other lines removed from them, take a small piece of paper and place it at the end of an open fitting on one of the relays. If the paper stays in place when you remove your fingers, there is vacuum leaking past the relay shuttle valve. Check the other three open fittings using this same method. If the paper doesn't stay in place by itself, there is not enough leakage to prevent adequate operation. You should replace any relays that show significant leakage.
You can also test your headlamp vacuum actuators by using the vacuum relay SUPPLY line to hook directly to either fitting on that actuator (manually bypassing the relay valve). Hooking to one side should open the headlamp; hooking to the other should close it. If the supply line has decent vacuum level (normal vacuum should be 15" Hg or higher; check with a vacuum gauge), the headlamp should quickly pop open and closed. This test can determine if the seals in the actuators are OK.
If the system doesn't have adequate vacuum, you will have to diagnose the problems and resolve them before you can solve any headlamp system issues. Just like anything electrical, you would need adequate voltage before diagnosing any specific issue with an electrical component.
Note: If there is little or no vacuum on these lines, there is a problem with the vacuum supply system.
With the supply lines hooked up to the relays...and the other lines removed from them, take a small piece of paper and place it at the end of an open fitting on one of the relays. If the paper stays in place when you remove your fingers, there is vacuum leaking past the relay shuttle valve. Check the other three open fittings using this same method. If the paper doesn't stay in place by itself, there is not enough leakage to prevent adequate operation. You should replace any relays that show significant leakage.
You can also test your headlamp vacuum actuators by using the vacuum relay SUPPLY line to hook directly to either fitting on that actuator (manually bypassing the relay valve). Hooking to one side should open the headlamp; hooking to the other should close it. If the supply line has decent vacuum level (normal vacuum should be 15" Hg or higher; check with a vacuum gauge), the headlamp should quickly pop open and closed. This test can determine if the seals in the actuators are OK.
If the system doesn't have adequate vacuum, you will have to diagnose the problems and resolve them before you can solve any headlamp system issues. Just like anything electrical, you would need adequate voltage before diagnosing any specific issue with an electrical component.
Last edited by 7T1vette; 08-09-2017 at 09:42 AM.
08-09-2017, 11:48 AM
#26
Burning Brakes
You can test your headlamp vacuum system while only using your existing vehicle. Have car idling in the driveway/garage; pull the vacuum lines off of one of the headlamp relays and determine which has vacuum on it; connect that hose to the center fitting on the relay (that is vacuum SUPPLY). Do the same for the other relay.
Note: If there is little or no vacuum on these lines, there is a problem with the vacuum supply system.
With the supply lines hooked up to the relays...and the other lines removed from them, take a small piece of paper and place it at the end of an open fitting on one of the relays. If the paper stays in place when you remove your fingers, there is vacuum leaking past the relay shuttle valve. Check the other three open fittings using this same method. If the paper doesn't stay in place by itself, there is not enough leakage to prevent adequate operation. You should replace any relays that show significant leakage.
You can also test your headlamp vacuum actuators by using the vacuum relay SUPPLY line to hook directly to either fitting on that actuator (manually bypassing the relay valve). Hooking to one side should open the headlamp; hooking to the other should close it. If the supply line has decent vacuum level (normal vacuum should be 15" Hg or higher; check with a vacuum gauge), the headlamp should quickly pop open and closed. This test can determine if the seals in the actuators are OK.
If the system doesn't have adequate vacuum, you will have to diagnose the problems and resolve them before you can solve any headlamp system issues. Just like anything electrical, you would need adequate voltage before diagnosing any specific issue with an electrical component.
Note: If there is little or no vacuum on these lines, there is a problem with the vacuum supply system.
With the supply lines hooked up to the relays...and the other lines removed from them, take a small piece of paper and place it at the end of an open fitting on one of the relays. If the paper stays in place when you remove your fingers, there is vacuum leaking past the relay shuttle valve. Check the other three open fittings using this same method. If the paper doesn't stay in place by itself, there is not enough leakage to prevent adequate operation. You should replace any relays that show significant leakage.
You can also test your headlamp vacuum actuators by using the vacuum relay SUPPLY line to hook directly to either fitting on that actuator (manually bypassing the relay valve). Hooking to one side should open the headlamp; hooking to the other should close it. If the supply line has decent vacuum level (normal vacuum should be 15" Hg or higher; check with a vacuum gauge), the headlamp should quickly pop open and closed. This test can determine if the seals in the actuators are OK.
If the system doesn't have adequate vacuum, you will have to diagnose the problems and resolve them before you can solve any headlamp system issues. Just like anything electrical, you would need adequate voltage before diagnosing any specific issue with an electrical component.
08-14-2017, 01:31 PM
#27
Burning Brakes
I checked the headlight relays today with a vacuum pump. When I pump up the relay you can here it slide. When I remove the vacuum you can hear it slide back. The same for both relays.
Both headlights will shut after I have opened them manually.
Both headlights will shut after I have opened them manually.
08-14-2017, 03:06 PM
#28
Team Owner
If you didn't use the vacuum from the engine, you really don't know how they will operate. Using a hand vacuum pump, you can isolate ONE component or one section of hose and have enough vacuum 'power' to evaluate the integrity of the hose or the seals in that one component.
But, without the amount of vacuum supplied by the engine, you can't test the function of ANYTHING with that hand pump.
Start the engine and do the hose swap tests I described to see what works and what doesn't. THEN you can focus on one component.
P.S. Just getting the shuttle valve to move in those relays won't tell you whether they will adequately seal vacuum to allow proper opening/closing of the headlamp buckets.
But, without the amount of vacuum supplied by the engine, you can't test the function of ANYTHING with that hand pump.
Start the engine and do the hose swap tests I described to see what works and what doesn't. THEN you can focus on one component.
P.S. Just getting the shuttle valve to move in those relays won't tell you whether they will adequately seal vacuum to allow proper opening/closing of the headlamp buckets.
08-15-2017, 07:42 AM
#29
Burning Brakes
I tested the relays with a hand vacuum pump. You could hear the relays open & close. I will try that with the engine running today to confirm the engine vacuum.
Last edited by LenWoodruff; 08-15-2017 at 07:54 AM.
09-22-2023, 10:28 PM
#30
Thank you!
Using this guide test each component and you will find the problem.
http://www.corvette-101.com/vacuum.htm
http://www.corvette-101.com/vacuum.htm
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