Cruise control Cruise light comes on. And turns green when set. But does not hold the speed

Could also be brake light switch or clutch switch if manual transmission as those pedal will disengage cruise if it is set the brake light switch would be worth checking fiirst

There is a vacuum leak in the hose that goes from the control unit to the engine intake manifold.

My guess is one of the following
The power not going to the cruise servo
Cable not holding
Servo failed
Switch failed

That's the cruise control. Green symbol means that it's enabled.

There is a double button on the tip of turn-signal switch. Pressing plus or minus freezes current speed and you may apply some relax to your leg. A speed tuning is possible using this button(s). There's also a switch that disables the feature. If you are forced to slow down or stop, you may run the car again and restore previously set speed using "Resume" function on this switch.

Cruise control switches immediately to manual control after touching the brake or clutch pedal.

Cruise control doesn't work at very low speed and is not recommended in streets woth heavy traffic.

Have you tried pressing the cruise control "on" button once then when you reach your cruise control speed press the "Set/Acc" button. The green cruise light should turn on then.

are you going uphill in overdrive gear . If the speed is lower than you set the crruise control might disengage. ?

The cruise control switches are located on the steering wheel. When the cruise control is turned on there will be a green light luminated on the dash that says "cruise". When at the desired speed press "set" to set the cruise control at that speed.

my BMW 740i has a problem with the cruise control.
The cruise control will work for about 20 miles and then quit working and will not work again.

First, your car must be in gear and driving approx more than 60 km an hour
Secondly, using the Cruise Stalk switch turn the Cruise on, the dash should now have a lit icon for cruise power (green).
Once you have the desired speed, gently press the button on the end of the cruise in to set your speed. Remove foot from throttle and confirm cruise is active. Another dash light should come on as well (orange)

Failing that, if it doesnt work the usual suspect like fuses and the brake pedal micro switch should be looked at...

Luckily, I have a 2008 Road King Classic (FLHRC) WITH a manual!

On the left handlebar switch housing there is a lever below the left turn signal button.
It should be flipped to the right for the cruise control to be on, left is off.

On the right switch housing, is a similar lever, below the right turn signal button.

When you're above the minimum speed (I do not know what this is, but 30 MPH is not fast enough for it to engage), push the lever to the right (towards the grip end). This will "SET" the speed.
If you hit the brakes, or accelerate above a certain rate, the cruise will kick off.
To get back to the set speed, when you're above the minimum speed, flip lever to the left to resume.

When the speed is set and engaged, to increase the set speed, flip right lever to the right, to slow, flip to the left.