CO alarm tweaking low power and No ceiling lights

Could be the CO2 alarm needs to be replaced they do have a use life usually around 7 years. Check the expiration date on yours, Is it 120 volt or 12volt. does it have a battery back up if so does a new battery stop the beeping. Do you have 12 volt at the light? could be bulbs are bad.

Do you know if the CO alarm is powered on the same circuit as the lights?

Check voltage at house batteries, Make sure the disconnect is in the CONNECTED (Use/ON) position, if you are plugged into shore power check converter and its breaker for proper operation, DO NOT TRUST eyes on circuit breakers, TOUCH them.

Then you need to start following the light..

With the RV not plugged in

Get a test lamp, this is a tool that looks like an ice pick with a plastic See thourgh handle, a light bulb in the handle and a wire with clip coming out of hte handle

Start at the batteries, Clip to one post (Negative?) tip to other LIGHT good

move tip to chassis LIGHT =bad ground

Move clip to chassis, touch battery positive to make sure you have a good ground and a bright light.. now move out along the positive wire. If you engounter any device, check both of the terminals (if it has 4 just the big ones)

As you move the clip, check back the last good test point to make sure you have a good ground still.

Problem exists between BRIGHT and Dark test points.

okay, update
Validated batteries are in series. reconnected put a meter to it and it reads 12V.

I don't have an inverters

The CO2 alarm still beeps low voltage and two ceiling lights still don't come on. However all of the other lights work in the bedroom including the closet. thoughts??

I think it may be the I had them in parallel. as far as output how do I know which one goes to ground and which one goes to positive (12 volts output).

You say coach batteries are new. Any chance you got 6 vole batteries connected in parallel? You would really have low voltage (6V) that way.

What about your inverter fuses?