There is a quirk to getting the S-Tec 50 autopilot to work in N75903

Step 1 – Move the Autopilot toggle switch (located to the right of the mixture control) to the TEST position

Observe all lights come on in the S-Tec control head

Observe the Trim UP light go Off

Observe the Trim Down Light Go Off

Step 2- Move the toggle switch to the center (ON) position

Observe all the lights in the control head go off except….

Observe that the READY light in the control head is now Green

At this time you may press the ON/OFF white button on the control head to activate the Stabilized (STB) wing leveler mode.

You can press in on the silver knob on the control head to activate the Heading Bug (HDG) mode

You may press the white NAV button to have the unit track either the #1 VOR or the GPS (depending on which position the NAV/GPS toggle switch is in ……………

You may press the white ALT button to have the unit maintain the current Altitude

Note that there are two disconnect buttons on the pilot yoke

The RED button disconnects the autopilot

The BLACK button disconnects only the Altitude mode