testing headlight switch
Thread Starter
Safety Car
Joined: May 2005
Posts: 4,176
Likes: 7
From: Jennings LA
testing headlight switch
what is proper operation for the vacuum part of the headlight switch? I have the switch and dash out and wanted test it before I put it back.
car is a 71
car is a 71
Racer
Joined: Jun 2002
Posts: 281
Likes: 0
From: Brookfield IL
Tonight I started testing my whole vacuum system- so I have a decent understanding of the components and how they work. Remember this one thing-- vacuum in the control system (headlight and wiper switches, manual overrides, etc.) keeps things FROM opening-- whether it is the headlights or the wiper door. When you want something to open, you block the vacuum in the control circuit, and by default things start to operate.
When the headlight switch is in the off position-- it allows vacuum to pass through the switch (because you are stopping the headlights from opening). Thus you should be able to put a vacuum pump on the vacuum source nipple, a vacuum gauge on the other nipple, and hold 30 in-Hg vacuum with no leakage. This proves the headlight switch does not leak vacuum in the off position. Seeing the same pressure on the gauge proves the two nipples are connected.
Take the headlight switch to the full on position. This should block the vacuum (disconnect the two nipples internally from each other). Disconnect your vacuum gauge from the other nipple and leave it open. You should still hold vacuum at the pump. This proves that the switch not only disconnects the two nipples-- but also does not introduce an internal vacuum leak.
You could do basically the same test to the manual override switches under the dash as well, as well as the vacuum actuator relays and vacuum actuators.
This is how I went through tonight and individually tested the actuators and actuator relays. To me it seemed a more logical starting point than running around with a vacuum gauge while the car was running. Especially since I figured the diaphragms (bladders) in these components are probably the most likely source of leaks.
Plus the pump allowed me to find leaks in the headlight & wiper door actuator relays-- even though they still operated ok. The wiper door actuator (gold can) diaphragm, on the other hand, was totally shot and didn't hold any vacuum.
What surprised me was that tonight I tested the vacuum actuator subsystem (the big hoses
), and so far found three sources of vacuum leaks (two minor, one major), yet my car does not idle at all rough. Maybe with the stock cam it generates enough vacuum at idle to compensate for the leaks? With all these leaks, I'm sitting at around 14 in-Hg at idle.
There are some good writeups on testing the vacuum system. But if people are interested, I could document my process as well.
Andy
When the headlight switch is in the off position-- it allows vacuum to pass through the switch (because you are stopping the headlights from opening). Thus you should be able to put a vacuum pump on the vacuum source nipple, a vacuum gauge on the other nipple, and hold 30 in-Hg vacuum with no leakage. This proves the headlight switch does not leak vacuum in the off position. Seeing the same pressure on the gauge proves the two nipples are connected.
Take the headlight switch to the full on position. This should block the vacuum (disconnect the two nipples internally from each other). Disconnect your vacuum gauge from the other nipple and leave it open. You should still hold vacuum at the pump. This proves that the switch not only disconnects the two nipples-- but also does not introduce an internal vacuum leak.
You could do basically the same test to the manual override switches under the dash as well, as well as the vacuum actuator relays and vacuum actuators.
This is how I went through tonight and individually tested the actuators and actuator relays. To me it seemed a more logical starting point than running around with a vacuum gauge while the car was running. Especially since I figured the diaphragms (bladders) in these components are probably the most likely source of leaks.
Plus the pump allowed me to find leaks in the headlight & wiper door actuator relays-- even though they still operated ok. The wiper door actuator (gold can) diaphragm, on the other hand, was totally shot and didn't hold any vacuum.
What surprised me was that tonight I tested the vacuum actuator subsystem (the big hoses
), and so far found three sources of vacuum leaks (two minor, one major), yet my car does not idle at all rough. Maybe with the stock cam it generates enough vacuum at idle to compensate for the leaks? With all these leaks, I'm sitting at around 14 in-Hg at idle.There are some good writeups on testing the vacuum system. But if people are interested, I could document my process as well.
Andy
