Just had an Osborne tip tank replaced on my 260 TC. I have fuel selectors similiar to the Twinkies: two selectors..L is 12 o'clock-->main, 9 o'clock-->tip, 6 o'clock-->aux., the Right side is the mirror image.
Prior to the repair, the two panel fuel gauges (appear to originals) defaulted to Empty when between detentes and when on Off (3 o'clock on L, 9 o'clock on R). Now they both default to Full in the aforementioned positions.
This is disconcerting to me, and appears to be a safety issue; during my scan I would tend to pass by a Full reading, especially since I'm used to seeing Empty as the default.
Of course, I use a fuel totalizer and clock as my main reference, but I can't ignore the gauges completely. Is this a mere wiring snafu, an unattached ground, or ?

Not sure about a 260, bit on my 250 there is a ground that causes the guage to read empty when in the off position so you don't think you are on a full tank. Maybe this wire is not connected and causing this change in your guage readings.

We think along the same lines, Wayne; I mentioned that a couple of weeks ago to the AI and he had considered that but wants to get a wiring schematic from Osbourne before delving into it.

On my twin the gauges read zero when sender wire is grounded and read full when sender wire is open. It sounds like your not getting a ground when between detents.