Lazy Daze Owners' Group

Hi Cheryl;  Lazy Daze used a yellow wire for a secondary hot lead. That tells you that there are other things connected to that fuse besides the LP detector. In this case the space heater. The manufacturer of the detector doesn't know that, so the red wire is good. They are both 'hot' but only 12v dc.
    That gray tube does contain a tubular glass fuse. Good because your old detector was beeping. You can leave it there. To look at it, twist the outer housing while holding the end that it isn't attached to the part you are twisting. You my have to slightly compress (make it shorter) to release the self locking.
    The dark blue plastic tubes are crimped butt splices. They stay.  Cut the wires just as they enter the light blue tubes. They are also butt splices, that connect the old  LPG detector.
    If you are going to use the Wago splicer devices. The hot yellow lead with the tubular fuse in line goes to the same  wago that the new LPG detector red lead goes to.  The other Wago device goes to the black wire of the new LPG detector, and the black wire coming from the dark blue butt splice.
    Energized for the first time, the new LPG detector goes through an extensive self test, and may take a few minutes before it stops alarming. You should be able to silence it during this wait. It might come back on.  After a while (3-4 minutes) it should stay on with a green light.  Good for 5 years (give or take a few months. I would write on the back the date you installed it. (for 4 1/2 years from now).

   A little history:  houses were wired with black wires for hot. Red dyes at the time turned turned black anyway. White as a 'surrendering flag' was safe as a neutral. Or in the old days a ground. Now green, bare copper (turns green with a patina), or really green as in ground with plants growing.  At the entrance to a house the ground wire is actually connected to the white wire, in the main box.
    Cars were wired with black as the ground (asphalt color?) and red as the hot lead. Pretty much still are.  Same things for 12v vehicles, the Lazy Daze is a vehicle. Modern items now come with white and red. Hot and ground. I think the florescent fixtures are red and white.
   But it is still proper, like your new LP detector, to come with red (positive) and black (ground or chassis common).
   You will need to strip some insulation off of the wires you cut off of the light blue butt splices. Try not to nick the small strands of wire inside the plastic. About 3/8" is good. The Wago connectors may have a strip gauge to indicate how much pvc insulation to remove. Twist the bare wire strands together to make it easier to insert into the wago.    RonB
   p.s., this is very orderly wiring. I've seen much much! worse.