Need Installation Manual for 400A Autopilot

[Rick Erwin]

Thanks Kevin, DM sent.

Rick

[Dan schultz]

I have the 1974 avionics installation manual let me know which drawings you need. I also have just the wiring diagrams from Cessna

Dan

[Rick Erwin]

Hi Dan,

I have ordered a 1977 Installation Manual for the 400A. If I strike out with the information in that manual, I’ll reach out to see if the information in your manual might help find the three wires I need information on is in yours.

Thank you for the offer!

Rick

[wslade2]

I have a paper manual for a system 400 (not 400A). Includes wiring diagrams. In case that’s any help or they share anything in common (don’t know if they do).

[n86121]

For the most part the autopilot is self-contained within its own harness.

For example, the 'Computer' gets continuous power from the aircraft through a circuit breaker. The control head switch closes a relay within the 'computer' to power it up.
All inside the 'computer'

I just recently got a full Avidyne suite,
and naturally wanted whatever autopilot capability I could get.

One of the mysteries was where/how to interface to a new IFD 550.

ANSWERS:
The autopilot gets its left/right guidance off the CDI.
It gets its climb descent rate by changing pitch on the control head
It holds altitude with an internal pressure sensor within the 'computer.'

I believe I found the schematic for that in the basic 337 electrical wiring diagrams.
Under, believe it or not, the AUDIO PANEL wiring.

WHAT?

The clue was the original audio panel had a DPDT switch to select 'OMNI 1 or OMNI 2"
It had two wires coming IN (for OMNI 1) that came from the original CDI.
As documented in the audio panel schematic.

I had the tech connect those two wires to the new CDI's similar outputs and PRESTO!
C'est voila!
Left right guidance from the new Avidyne avionics.

[Dan schultz]

There are five wires to connect to the autopilot controller. I am out till late he 15th. I used Approach Fast stack for my wiring harness. My GNS530W is connected to the 400A. I can tell you the wires to connect when I get back.

Dan

[n86121]

I don’t think my 69 T337D AP has any external inputs for pitch etc.
Except from the artificial horizon or small control head.

It may just be an “A” model?

AP has the small control head center stack down by pilots right knee.

Control head has a heading bug there, as well as pitch / turn center and controls.
Also has an altitude HOLD switch.
Activates pressure sensor in computer to “hold” altitude
At whatever pressure altitude present when switch is flipped.

If there is a vertical interface, that would be interesting.
Not critical, but interesting.

As you know 337 so stable, barely ever use AP.

[Learjetter]

Originally Posted by Dan schultz

There are five wires to connect to the autopilot controller. I am out till late he 15th. I used Approach Fast stack for my wiring harness. My GNS530W is connected to the 400A. I can tell you the wires to connect when I get back.

Dan

Dan, I’m quite interested in your 530w solution as I also have 400A AP working fine in HDG but apparently not functional in NAV(GPSS). Look forward to your return!