High-low vacuum pump light

[Greg_D]

On 1/16/2019 at 9:51 AM, Awful_Charlie said:

The spare KI256 I have on the bench has the switch on the end of a hose roughly 8" long, and then about 3' of electrical wire hanging off that.  The hose for the switch is a smaller diameter than the other two fittings on the back of the horizon. In the aircraft, the KI256 fitted doesn't have a switch at all! I want to add this in, but am having trouble finding the connector on the main loom into which to plug it - any hints gratefully received!

Here are a couple shots of the back of my KI-256.  Any idea which hose has this magical adjustment pot and wires attached to it?

[Awful_Charlie]

The small tube on the right in the first pic, and at the bottom in the second - at the end of that I would expect you will find the switch pictured earlier in the thread

[Greg_D]

I thought that I would  post a follow-up on my search for the pressure sensor.  It was at the bottom of the hose that Charlie pointed out.  And there was an adjustment pot on the sensor that fixed the problem.  Thanks for all the help everyone.

[carusoam]

Great detailed follow-up, Greg!

Thanks for sharing the details and pics.

Best regards,

-a-

[Awful_Charlie]

On 1/16/2019 at 4:51 PM, Awful_Charlie said:

.... I want to add this in, but am having trouble finding the connector on the main loom into which to plug it - any hints gratefully received!

 

On 5/1/2019 at 3:01 AM, Greg_D said:

I thought that I would  post a follow-up on my search for the pressure sensor.....

 

 

Any chance you could give me a hint where the wires go to from the switch? From the wiring diagram I know they go into the main loom, but there's a lot of that! Anything along the lines of "Behind instrument x" or "into the massive bundle of wires with the current monitors" would be a help

[Greg_D]

On 5/2/2019 at 10:43 AM, Awful_Charlie said:

 

Any chance you could give me a hint where the wires go to from the switch? From the wiring diagram I know they go into the main loom, but there's a lot of that! Anything along the lines of "Behind instrument x" or "into the massive bundle of wires with the current monitors" would be a help

I can't really see where the wires go other than that big bundle of wires you mentioned.  I know there's a circuit breaker on my breaker panel for the unit though.

[Awful_Charlie]

Thanks - I'll go for a hunt in there. I was hoping it would be just about anywhere else!

[Awful_Charlie]

OK, so I found it after a too much time lying on my back with my head on the rudder pedals. Odder and odder! Since I bought the aircraft, the vacuum light has only ever illuminated with the test button, and never any other time. When I swapped the KI256 out, the one that came out had a blanking plug where the switch was connected to, and the replacement had a tail of hose with a switch on it, so I had *assumed* that the original horizon just didn't have the switch at all, and hence why the light never came on. After pulling apart the ty-wrapped bundle of wires, I finally found the connector, but it already had a socket attached to it! Chasing that through and I found a pressure switch on a stub hose from the vacuum regulator itself, and that had one lead of the three disconnected. It was going to be a right ba**ard to get the other wire onto that by virtue of its location, so just moved the wires onto the switch plumbed into the replacement horizon - tested ok (for low vac only - I couldn't think way to create a high vacuum source easily)

a w

View looking upward and outboard from behind/under the panel near the centre - the corrugated demister hose is visible in the top left and the vacuum regulator at the top just right of centre