Cruise control on a 2002 Ford Ranger?

Sometimes the cruise control will not engage… If I tap the brakes, it will engage, what causes this and how can I fix it?

Added (1). I was a bit vague, If I go to set the cruise control at my desired speed, the cruise won't engage but the little green light on the dash will flash, as if it is trying to… Its when I tap the brakes then press the set button again, that the cruise will engage…

The cruise control should not engage with the tap of the brakes - it should disengage. To me it sounds like you have a faulty switch that is supposed to turn of the cuise control system or set the cruise speedl. It's just coincidence that taping the brakes SEEMS to fix the problem when it acutally does not. You could have a faulty actuator in the throttle linkage that sticks or binds up.

The cruise control is designed to disengage (or to not engage) when it detects the brake pedal is being pressed so another possibility is that your brake switch is sticking and needs to be replaced. Tapping the pedal might be freeing up the failing switch.

Have you had anyone follow you in your truck recently? If not, have someone follow you and see if they notice your brake lights being on when they shouldn't be. If so, your problem with the cruise control might be solved by simply changing out the brake switch that physically touches the brake pedal or the arm attached to it.