Installed a universal fan light on our hunter ceiling fan that has high light, low light, and off. It cycles through the phases without being touched. Drives us crazy.
How to fix it?

My first thought is to return it to the store as defective.

Since you have provided no information on the model of the light pack or the installation instructions we are at a loss to help you.

How does the light pack connect (electrically) to the fan? How is the light pack supposed to work, from a wall rotary switch, remote control?

If it has a remote, try removing batteries.