My marine kohler only runs when the starter button is held down.

If this were 1975, I'd say it was the coil resistor.

What model?
Link to manual?

Hello, I have kohler 7.3 ecd generator and it's starts and then stop's. It says "UU" that means low voltage but I measured the voltage it is 232V ( I think it's not low voltage) but it's stop and say UU. And sometimes its says low water pressure but usually low voltage. Water is running great.

Larson Check your power coming to the coil.
Check it with key in run position .
When you crank the engine it gets power from a diff. prong on the key switch , then when you release the key it comes back to the main power feed.
You could have a bad key switch or a loose connection.
LUCK