That shouldn't be any problem at all. I have 3 fans spliced into my cabin light circuit; they draw .5 to 1 amp each. The circuit breaker on the panel is sized to protect the wiring itself; it wouldn't even notice the additional draw of your tank monitor.

I concur. Just make the splicing neat and well sealed.

FYI, I've used an in line splice from Ancor that is easy to use and neat. You insert the wires into holes in the end, then close the cover and squeeze. No stripping involved. Don't know the exact product # but it's in their catalog and I believe I got a package from West Marine or Boat US. I got the idea when I looked in the cabinet above the sink in the head; Catalina used them to splice in the light below the cabinet.

The wiring going to the tank sensor from wherever you splice in to the cabin lighting is probably very small gauge, say 18 ga or 20 ga. The wiring from the distribution panel going to cabin lighting is probably considerably heavier gauge than that, probably 14 ga, or at least 16 ga, I would imagine. The circuit breaker is sized to protect this larger gauge wire.

Ask yourself 'What If?'

WHAT IF the tank sensor internally shorts, will the cabin lighting circuit breaker pop before the tank sensor wire burns up, and thus burns up your boat? Answer: without an inline fuse protecting the smaller gauge wiring, if the sensor shorts the small gauge wire will burn, start a fire, and...adios boat.

You must make sure the smallest gauge wire in a circuit is properly protected by adding an inline fuse at the point where the tank sensor wires spur off of your source circuit.

Maybe I'm missing something here, but doesn't the gauge have to be wired to the device on the tank, or is it wireless? If it has to be wired, then you have to run wires anyway, no?