Need Pic of trim/ap wiring plug

[Melliot]

We bought a 77' P337, and AP hasn't worked. Just trying to track down the issue. First thing I've found is this plug and circuit board with 3 wires broke off of it as the yoke was hitting the wiring harness. I was hoping someone could take a picture of there's so I know what color wire goes to what point on the board. Only 3 wires are broke on mine. The wiring diagram in the manual doesn't specify nor does the Cessna 400A manual. Just need a Pic please. I'll troubleshoot more after getting all 3 wires soldered back.

[RandyArizona]

Originally Posted by Melliot

We bought a 77' P337, and AP hasn't worked. Just trying to track down the issue. First thing I've found is this plug and circuit board with 3 wires broke off of it as the yoke was hitting the wiring harness. I was hoping someone could take a picture of there's so I know what color wire goes to what point on the board. Only 3 wires are broke on mine. The wiring diagram in the manual doesn't specify nor does the Cessna 400A manual. Just need a Pic please. I'll troubleshoot more after getting all 3 wires soldered back.

What you are looking for, (I believe), is the Avionics service/parts manual.
D4548-2-13
I have a set for the 1974-1976 models.
If you give me a little more information, I may be able to track down the pages that you need. (the 76-77 models were almost identical)
I will need autopilot model.
The plug and circuit you are looking at, is the board that the wiring goes thru / to the yoke, and then to the items, (ie, ap disconnect/map light/ptt switch)
Let me know, I will attempt to photocopy the pages you need.
Regards,
Randy

[RandyArizona]

The item you show in the picture, is listed at
parts manual
FIG 94A
Items are
36 3421-0000 connector socket
43 S1961-1-0 Housing
44 1570306-1 board-circuit
45 3428-1002 header

From my quick look at the avionics manual, and wiring diagrams,
it appears, the mechanic chooses the wires he uses from the connector and header. I don't know. The manual is vague.

[Melliot]

Yes, that seems to be what I need. I have a 1977 T337G. Cessna 400A autopilot. Not sure if those wires would effect the ap or not. Electric trim still works. Thanks for any help!

Originally Posted by RandyArizona

What you are looking for, (I believe), is the Avionics service/parts manual.
D4548-2-13
I have a set for the 1974-1976 models.
If you give me a little more information, I may be able to track down the pages that you need. (the 76-77 models were almost identical)
I will need autopilot model.
The plug and circuit you are looking at, is the board that the wiring goes thru / to the yoke, and then to the items, (ie, ap disconnect/map light/ptt switch)
Let me know, I will attempt to photocopy the pages you need.
Regards,
Randy

[Melliot]

Yeah, that's the kicker. I may just have to rewire the whole thing or see if those wires that are broke do anything anyway. I was hoping it was standard wiring and I just didn't have the diagram.

Originally Posted by RandyArizona

The item you show in the picture, is listed at
parts manual
FIG 94A
Items are
36 3421-0000 connector socket
43 S1961-1-0 Housing
44 1570306-1 board-circuit
45 3428-1002 header

From my quick look at the avionics manual, and wiring diagrams,
it appears, the mechanic chooses the wires he uses from the connector and header. I don't know. The manual is vague.

[RandyArizona]

Give me a few hours, we’ll see what we can do for you.

[rustymwm]

The attached files are from the 77-78 Avionics manual D4580-2-13.

In order for the autopilot to power on, pin A on the control unit must be grounded. It is certainly possible that one of your broken wires is the cause of your dead autopilot.

Since your electric trim is functioning, pin D on the trim switch is properly grounded. Thus, the problem could be: 1) the autopilot disconnect switch on the yoke is not closed, 2) the g-switch is open, or 3) there is a fault in the associated wiring - probably one of your broken wires.

As you can see on the diagram, the color code for the wire on your circuit board is yel/grn (1). I could not identify this wire in your picture. If you cannot identify the wire based on the color code, an alternative method would be to use a multi-meter. With the AP powered off, there should be little to no voltage on the wire. With the AP powered on, there should be near 25V on the wire. Note: You will have to hold the AP power switch "on" when you check the powered on state of the wire. If the switch stays on by itself, then forget all of the above - it is not the problem.

As for the other 2 wires, since the pitch trim works, they could be related to either the mic push-to-talk switch or the map light on the yoke.

Hope that helps.

[RandyArizona]

I was beaten to it.
Attached are what I have.
"like a chinese buffet, take what you want, and leave the rest..."

[RandyArizona]

Last pdf file of the autopilot

[Melliot]

You all are awesome! Thanks and I'll see what I find when I get home.

Originally Posted by rustymwm

Attachment 3076

The attached files are from the 77-78 Avionics manual D4580-2-13.

In order for the autopilot to power on, pin A on the control unit must be grounded. It is certainly possible that one of your broken wires is the cause of your dead autopilot.

Since your electric trim is functioning, pin D on the trim switch is properly grounded. Thus, the problem could be: 1) the autopilot disconnect switch on the yoke is not closed, 2) the g-switch is open, or 3) there is a fault in the associated wiring - probably one of your broken wires.

As you can see on the diagram, the color code for the wire on your circuit board is yel/grn (1). I could not identify this wire in your picture. If you cannot identify the wire based on the color code, an alternative method would be to use a multi-meter. With the AP powered off, there should be little to no voltage on the wire. With the AP powered on, there should be near 25V on the wire. Note: You will have to hold the AP power switch "on" when you check the powered on state of the wire. If the switch stays on by itself, then forget all of the above - it is not the problem.

As for the other 2 wires, since the pitch trim works, they could be related to either the mic push-to-talk switch or the map light on the yoke.

Hope that helps.