I have searched the manuals but can't find the answer to this:  

If I only install waypoints using the ADEU the autopilot will fly the INS route.  If I install both a flight plan and ADEU route the autopilot flies the GPS route.  

Is there a way to have both the ADEU and FS9 flight plans but have the autopilot fly the INS route?

As an example, I downloaded the ADEU and FS9 flight plans Mumbai to Franfurt.  When I engaged the autopilot by activating it, then changing the knob to LOC and hitting the GPS switch, it followed the GPS route of the FS9 flight plan.  When I turned on the heading hold switch it changed course to the heading marker.

Installing only the ADEU flight plan and not activating the FS9 flight plan that was part of the Mumbai-Frankfut package, I activated the autopilot, changed the knob to LOC and hit the GPS switch, it followed the ADEU flight plan.  The course heading marker showed the wind corrected heading, as it was supposed to do.

How can I have both installed but keep the autopilot on the INS route?

Hi Gianfranco,

Thanks for your usual fast reply and assistance.  I forgot to write that I am flying the CS Legendary 707 with the old style autopilot/flight director.  When you say to use heading mode, I understand on the 707 AP/FD that means engage the toggle switch entitled "HDG SEL" (Heading Select), and leave the mode selector in "Man" (the choices are MAN, NAV LOC, AUTO GS and MAN GS) correct?

The 707 manual describes the HDG SEL function this way:

HDG SEL(HEADING SELECT) SWITCH
– When engaged the autopilot will turn the aircraft to (the FD shows the way) and hold the heading selected
on the captain’s present heading selector. Effective in MAN and NAV/LOC mode prior to course capture.
Switch trips to OFF when the AP is disconnected (Z-button or as assigned), or when the AUTOPILOT TURN
AND PITCH CONTROLLER is used to control ROLL. The sequence HDG SEL SWITCH – ON, GPS light +
NAV/LOC - PUSHED moves the FD and the airplane will then turn to and track the selected FSNAV route
course (track).

Ah, okay, that explains things.  Last night I tried all sorts of combinations of AP/FD settings and nothing would lock  the FD to the INS.  I didn't have time to experiment yesterday, but I'm sure in the past (I've been operating the INS for about 4 months) if I do NOT load an FS9 flight plan and either manually load checkpoints to the INS or use ADEU, when I select LOC and press the GPS button on the 707 AP/FD and the HDG toggle, the FD will lock on the INS course.  I guess when there is no GPS/FS9 flight plan available FS flight direction defaults to the INS.  

Thanks again for your help, your fast responses are extraordinary!