i was quickly dissatisfied with the battery/water tank sensors that came with my Rockwood Mini Lite 2304 KS. Water tanks gave random readings even before the black water tank was "christened". And the battery showed low charge even though my multimeter at the battery and at outlets said full charge.
So, after Youtube and forum research, I installed the SeeLevel II tank sensor monitor system. The model I installed was the 709 P3, from Amazon. Warning now...check your tank depths where you want to place the sensors. I had to buy the smaller "JS" version of the sensor cards because my tanks are rather narrow. Experimented with the standard sensors first including cutting them to fit, so I could not return them. My loss is your benefit!
The hardest part of the install was figuring out the wiring at the control panel. I removed the old POS indicator circuit board and worked thru the wiring. As indicated in the instructions and vidioes of similar installs, all the sensor data comes across one data wire for all 3 tanks. I chose the blue wire from the old install and basically set up the fresh water tank first to work out the wiring. Disconnected all the old probe wires at the tanks and abandoned them except for the blue and ground wire at the fresh water tank. Used the blue wire at the tank as the new sensor wire and reused the ground wire at the fresh water tank as the sensor ground wire. For the other two tanks (after testing the fresh water sensor wiring worked), I bought rolls of 16 gauge blue wire and white wire and then extended both the sensor and ground wires to the new sensors to be installed on the other two tanks.
At the panel, it was trial and error finding the right ground wire that connected with the sensor and vehicle ground. Used the power wire that served the old monitor circuit board.
Other big challenge was figuring out the water pump wiring. The SeeLevel instructions were useless, with no wiring diagram or description of wiring the pump, just calling the white wire on the new monitor wire harness the "pump indicator". The real BS here is that on other models of the SeeLevel, there is a yellow wire that those instructions say is power for the pump. NOT SO ON THE 709P3 MODEL!!! Unlike every video on Youtube where other models are featured, you actually have to wire up the Pump Switch as well as the monitor wire harness. No documentation on this!!
In addition, my water pump documentation says it requires a 10 amp curcuit, and the SeeLevel II instructions are adamant that you must use a relay if your pump requires more than 7.5 amps. So I had to also install a re!ay. Bought a 4-terminal fog light relay from an auto parts store rated up to 30 amps.
I noted the wires on the old water pump switch and then removed the wires and removed that switch (pump switch is already on the new monitor board and I needed the space to screw the new tank monitor onto the old control panel).
The pump switch and relay are wired thusly (double check your pump switch for continuity to make sure you know which positions for the wire to the relay and the ground wire)
Monitor wiring harness:
Red wire: power supply (I used power wire that served old battery/tank monitor)
Blue wire: blue wire to the new fresh water tank sensor (other tank sensors ganged to this wire underneath the trailer)
Black wire: Ground (note the ground wires in the trailer are generally white)
White wire: to the ground side of the new water pump switch, which is also connected with the vehicle ground.
Center switch terminal: 12 volt power supply (with fuse placed in this line) can be same power supply as the serving the red wire on the monitor board wiring harness.
Bottom switch terminal: line side wire to Relay Terminal # 86
Top (negative) switch: ground wire. Tied to white wire from monitor wire harness
Relay (standard terminal numbering, but check your relay)
#30 terminal: large gauge red power supply wire (previously fed power to the old pump switch
#87 terminal: large gauge wire to the water pump (previously the line terminal on the old pump switch)
#86: wire from the line side of the new water pump switch on the tank monitor board)
Mounted the relay above the control panel, inside the cabinet wiring space.
Much testing (and several blown 15 amp fuses at the main fusebox as I figured out the pump wiring) to make sure the fresh water sensor worked (monitor has a diagnostic mode where you can check the signal strength and number of sensor segments being used). After this worked, I extended the blue sensor wire and the ground wire from the fresh water tank to the two waste tanks. You cut out small tabs in the sensors so they know which tank they each are monitoring.
For the waste tanks, the instructions say the sensors need to be some distance, 1-2", away from metal. Since the old waste tank probes were so close to where you would mount the new sensors, I chose to mount the waste tank sensors on the opposite side (passenger side) of the tanks. The tanks are not as deep on this side, but plenty of room for monitoring contents.
Finally, all wiring tested and sensors permanently mounted using their adhesive backs.
At the control board, I used a dremel tool to cut out the center of the old battery/tank monitor are (plastic board) to mount the new monitor board. Pretty good fit.
One gremlin found. When I turned on the LED light at the dinette (there is a wiring raceway right above it where the tank sensor wire runs) the LED light created interference and blocked the sensor signal. Did some research and found that ferrite chokes installed around power wires stop this interference. The raceway has a narrow depth, so ordered a pack of 10 small ferrite chokes (they look kind of like fishing weights with 3 mm center openings. Lowered the LED light from the cabinet and started snapping ferrite chokes around the power and ground lines of the light. Took 3 chokes on each wire (didn't test to see if you only needed them on one wire) to kill the interference. Add one more on each LED light wire for good measure. The wires with the chokes fit fine back into the raceway. No more interference from this light.
Here are some photos of the installed monitor system and the ferrite chokes that fixed the interference issue.
BTW, after the install I mounted a switch for my Weboost 4G-M cellular booster so you see that on the control panel now.