monitor panel black tank display

I assume (dangerous, I know) by your last post you have not put anything in the black tank since you changed the probes, correct? This pretty much eliminates them as the problem. I would look at as much of the sensor wiring as you can see to make sure nothing is chafed and/or shorted to the frame or another wire. Also, something may have failed in the "red thing" which is probably the electronic circuit which reads the probes and lights the lights. I don't know how to test this or where you could get another one. Maybe someone else can help you with that. You could also add something like the SeeLevel tank sensor system which is supposed to be pretty accurate and trouble proof but that is $$$.

Hope this helps.

Ken