SOLVED No 12V

To get a good answer, give a little information about your RV. There might be someone on here with the same year/brand/model that's already run into your problem and fixed it.

You may have what's called a "salesman's switch" next to your entry door. It's meant to reduce the battery drain of RVs while they're on display.

Have you checked the battery? Cleaned the connections?

Winnebago Brave SE 2001 29A. Battery have power. Check the connection. The one switch, by the door is AUX Battery and I try to turn on and off. Nothing. I can hear a solenoid clicking on front.

Sounds like battery disconnect is in off position.
Should be switch normally by the entry door to energize battery disconnect relay. Some Winebagos have battery disconnect behind the entry step. As I remember that is wwhere your batteries are. There is a small metal plate to remove to show disconnects.
Sounds like blown fuse. Some battery disconnect relays have fuse mounted to them.

My batteries are under the step. I look everywhere and can not see any master switch. I trace the Positive wire(big)from battery and could not find any switch. Could it be that the relay give up?.

I run jumper cable to control box and have 12V in coach. Lost connection somwhere between battery and control box.

Yes, it could be relay or blown circuit breaker.
Go to Winnebago website and locate the electrical drawing for your rig.
Option is to follow the positive cable.
Relay could be in the battery control center depending on which one you have.

The relay is in front of vehicle. I can hear it clicks. Will the 10gauge wire be enough for temporary jump?

There is usually a fuse right at the battery. It is like a 250a or 300a fuse. That could have popped

Very temparary.
Circuit breaker at or on circuit would normally sized according wire size leaving batteries going to the converter. I would guess closer to a 30 amp.