The fuel gauges on my 260C are irritatingly poor. I have tried to ‘calibrate' them with little success.Mine us the type with two gauges and a switch to toggle between left tanks and right tanks. It might be that my two capacitors (that attach to the inside of the firewall) are not right, as they are not marchetti parts.
Is it an option to go to capacitive type transmitter? Does anyone have experience.
I can only talk from my experience when installing an EDM900. before I had the same issues.
1st measure the resistance of the transmitter by moving the swimmer. it should be approx 0-38 Ohms (no - to full fuel)
2nd I removed the transmitters and opened them. there is a small finger running over a kind of spool. Take care when removing the cover, better not bent the cover holding pins, they´ll break. after cleaning and replacing the plastic type washer on the transmitting cable into the tank cover it ran really smooth and indicated a correct resistance.
3rd the transmitters are connected under the co pilots back seat, those connectors where very coroded on my plane. I changed the complete cable from under the seat to the panel, but believe you´ll do good when cleaning the contacts and reassemble it.
from my experience the cables, inside the plane and to that switch are good enough, didn´t find any break on that.
I remember there was an extra ground connection at the switch.