71 Headlight Switch Vacuum Question

[Peter B.]

I have a 71 and when the lights are off, there is a huge vacuum sound from the headlight switch. When I turn it on it sounds like the vacuum is getting passed through to the other vac line attached. However, when it is off, is it normal to have this huge vac noise or should it be a sealed "off vac" function.

Any help is greatly appreciated.

Also, if anyone has the time and could explain the relationship between the vac switch on the headligh switch and the by-pass switches, that would be great.

[Roberto L.]

Re: 71 Headlight Switch Vacuum Question

Hello, the vac headlight switch open and close headlight doors when lights go on/off (normal use) while the by pass switch open/close headlight doors even with lights off, hence the by-pass term.

Roberto, NCRS #30019, RMC

[Jack H.]

Re: 71 Headlight Switch Vacuum Question

Vac supply enters the cockpit from the second nipple on the check valve and through the firewall. From there, this vac control line T's to power the WSW wiper door control, the headlight switch and ancillary vac functions like A/C control valves, wiper door & HL door over ride switches, Etc.

It wouldn't be the first time one or more of the various vac control switches was leaking (hence a general noise from behind the main instrument cluster) OR some prior mechanic working on the car failed to route the various vac lines properly or get them connected nice and tight on their various switch component nipples.

You should hear NO noise from behind the instrument cluster. If you do there's a problem and it requires: (1) understanding the vac circuit topology, (2) verifying all routing paths are correct, (3) individual vac switches are functionally intact, and (4) may well require the odious chore of dropping the steering column and pulling the speedo/tach instrument cluster to gain access.

If you wind up having to pull the cluster to fault isolate, READ the Chassis Service Manual for step by step instructions!!!!!!!! The main electrical wiring harness is clipped to the backside of the instrument cluster and if you simply use a 'big hammer' approach to pulling the cluster there's a clear and present danger of the hold down clip 'sawing' into your electrical harness....

[Peter B.]

Re: 71 Headlight Switch Vacuum Question

Thanks!!!!!!!!!!!!!