33 minutes ago, Z Excellence said:

When I pulled out the center console and with one hand I would touch the vacuum selector Lightly with my finger While vent was selected  it would cause air to come out different areas. 

I used to know somebody that was convinced that their body was magnetized because their watch battery died often.  Kidding!!  (Actually I did know somebody that told me that).

I don't know how a touch could cause a mechanical valve to switch like that.  Who knows.  I know that the flappers have a spring that has to be overcome by the force of the vacuum.  Maybe yours were right on edge.  Brushed a hose or something.  I notice that those nipples and hoses seem to be of different diameter, so if they're switched one would be loose and one tight.

These cars are like Alice's rabbit hole.  Always more to explore.  That sounds awkward...

Not really. 

I've had my car for 40 YEARS and still finding more rabbit holes to explore.

14 hours ago, zclocks said:

Good catch Zed...

 

I have a 75 and this is what the manuals says . The "T" in the vacuum line  should be connected to the D1 on the vac switch , but is connected to I.

That is exactly how mine is connected. I is connected to D1.  1976 280Z manufactured 9/1975. 

Maybe the vacuum switch halves are loose. Touching it changes the way the halves meet each other?

That’s exactly what I was thinking! Can’t find vacuum valve anywhere. 

If you can remove it maybe it can be repaired. Never heard of one going bad , but after 44 years who knows.

Fastwoman did an excellent thread on rebuilding the vacuum selector valve here and well worth doing while you are there.  

 

I did get a photo after mega contortions, but my 75( 1/75) is connected as per the manual.  D1 hose to D1 on valve  and "I "hose to " I "on valve. "T" connection is from D1

 

You can see how somebody going by memory of working on a Z in the past might put them on the wrong nipples.

Looking at the two side by side looks like the the switch labeling is different in Z Excellence car than mine. Mine matches my manual. 

 

1 hour ago, zclocks said:

I did get a photo after mega contortions, but my 75( 1/75) is connected as per the manual.  D1 hose to D1 on valve  and "I "hose to " I "on valve. "T" connection is from D1

 

Thanks for your time in doing that to help me. It was super hard to get down there twisted to even take the picture I know. I’m 66 and once I got down there it was hard to get out!!!

Ha  Ha!!  I'm laughing cause I have the same problem and  I'm older than you. Thank god I have a pull out radio.