Our Motorhome has a SeeLevel I, not the newer SeeLevel II, tank monitoring system.
It's hard to find good info, but it would seem the sensor sends a value between 0 and 5V, with linear progression, to show the level. 0V is empty, 5V is full, 2.15V is 43%
I got this info from this manual:
Garnet SeeLevel I Tank Monitor Accessory
That document also mentions the sensors have 1,000 Ohm internal resistance.
I believe we have the Model 707 SeeLevel I (Documentation HERE)
It would seem this system uses the 12V it gets from the RV to power the display, and read the 0-5V values from each of the tanks. Is there a way to read out those values via a CerboGX or similar?
It is my understanding that the newer SeeLevel II system, that DOES have an N2K variant, can work with GX, but I think that would also require new tank sensors to be installed (which I want to avoid).
With lots of older high-end motorhomes being bought by younger couples, I hope someone can find a way to convert SeeLevel I to interact with a CerboGX or VenusGX.