Here's a different post from a different forum, but you might be able to glean guidance from it.

https://www.triumphbobberforum.com/threads/solved-diy-cruise-control-issue-is-there-something-missing-on-my-bobber.18754/

 

It is relatively usual the cruise control to be deactivated by ECU if there is any underlying system error.

It acts that way as a safety control for eventual problems.

First of all you should check error registry. Best is if you can use some system like TuneECU or DealerTool. If not available, you can reach the registry by keeping pressed the "i" button on the left handlebar controls while switching key on. After a two or three seconds you will see the text "dtc" in the dash, followed by eventually an error code (or P000 if no errors). A short press on "i" moves between different codes if multiple errors (there will probably be more than one, one being P1574 (that code means "cruise control deactivated by other errors").

You will probably see a code that gives indication of what failed. After fixing whatever and clearing the code (it also clears by itself after three full engine cycles - moving the bike enough to run from cold to full temp), you will usually recover the cruise control.

If you see code P1575 means a full deactivation of cruise control. That happens after a series of errors that affect the driving electronics. That is supposed to need an adaptation reset by OBD2 and follow a series of actions on controls.

 

The brake light switches also kill power to the CC thru the ECU. You should have 12V from the switch to the ECU when brakes are released. 0V when applying brakes.

 

Using front or rear brake, pulling on clutch lever or moving the throttle grip very much (+ or -) will disengage cruise control. First thing I would check is to make sure the front and rear brake switches work properly, that's often a reason why CC fails to operate. If you have a switch that is sticky and doesn't turn off the brakes when released CC will not operate. Just turn the bike on and operate front and rear brakes and make sure brake light works as intended. If those are ok move to the clutch switch and make sure the plunger is moving in and out when you pull the lever. They can get sticky or, rarely, get broken off.

 

He said the icon stays lit, on my T120 when I touch anything to deactivate the cruise the icon light goes out. The fact that it stays on is a little bit puzzling.

 

Just turn the bike on and operate front and rear brakes and make sure brake light works as intended. If those are ok move to the clutch switch and make sure the plunger is moving in and out when you pull the lever. They can get sticky or, rarely, get broken off.

The switch can operate the brake light just fine and also be faulty in the other position that sends power to the ECU. Each switch has 2 separate contact points. One switches the brake light on and off, the other switches the CC on and off.

He said the icon stays lit, on my T120 when I touch anything to deactivate the cruise the icon light goes out. The fact that it stays on is a little bit puzzling.

I assumed he was referring to the "cruise" icon coming on after the button was pushed once and not the "cruise set" light that comes on after the second press.