First, welcome to the forum from Pa. What year and model bike are you riding? On my previous rides I believe two things controled the duration of the turn signals. One was distance traveled and the other was the angle sensor which turned off the signal after a turn. Other than that the signal stayed on unless I turned it off manually.
I am riding a 2008 1800. The manual says approx 210 yards or 7 secs, I believe. The angle sensor applies after you make the turn. If I bring the bike to a full stop before the yardage or time is up, the signals will flash until I turn them off or until I complete a turn. Since I do most of the leading of my riding group, I would like to be able to have the turn signals flash longer than seven seconds or two hundred yards so that my following riders have plenty of time to see what my intentions are.
The only thing I could find posted on the net was this comment:
The "Speed Cancel Switch" is located just above the front tire. It is in the stem, at bottom, and is easiily accessed by unhooking the back of a black plastic cover. Once there you will find a clip that is about two inches long that is hooked to the body by one screw. Take the screw out and remove the clip and you should have it inoperative. Make sure that the switch is in the netural position, pointed toward center of bike. The other end of the clip slips over a little black slot to move the ancel switch when you cut the wheel..
These instructions are not very clear and were posted for a GL1500. I don't know if they are the same for a GL1800. Also, it sounds like you are basically disabling the automatic shut off feature which I'm not sure you really want to do.
Sorry, I couldn't be more help. Perhaps someone else on the forum can be of assistance.
I checked the maintenance manual and the 1800 has a completely different location for the turn signal cancel unit. In the 1800, it is inside the left fork. A bear to get to just to look at it. In any case, there does not seem to be a way to adjust the cancel signal duration, unless there is someone out there who manufactured a circuit board that would do what I am looking for. This all may be just too hard for the results.
To disable the system cut the white/black wire (speed sensor signal) going to the turn signal cancelling unit. If you want it working for some riding conditions and off for others install a switch. On the 2010 model 1800 the turn signal cancelling unit is inside the steering stem.