I have a 2001 u320. Guage is broken that shows fresh water, black water, propane etc. where can you buy the guage. Foretravel doesn't stock them anymorr
You will likely be better off buying a SeeLevel system, many have changed to this as their 20 year old unsupported OEM system fails.
You need two sensor strips for each tank if you want full coverage. Many buy two kits, each comes with three strips, and then they have a display inside the coach and one in the wet bay. Search for SeeLevel on the forum.
This web site store usually has pretty good prices.
Garnet 709 SeeLevel II Tank Monitoring System (https://www.rvupgradestore.com/Garnett-Technologies-Model-709-SeeLeveL-II-p/709-1003.htm)
If it's the original, you can't - they aren't available. As Roger mentions, the vast majority go to a SeeLevel system.
Jpettigr, send me a PM if you want, we have the same coach (mine is a 36') if you want some installation ideas. Pretty easy in this coach.