I should probably have checked my clamp / swivel was designed for a trim sender before I bought the trim gauge.....
Anyhow, it's one of these
Unopened boxed, if a little dusty.
Anyone got an hour meter, pressure gauge (for cooling water pressures) or temp gauge of a similar style they want to swap? I have no alarms on the engine, so any or all (depending on the condition!) of them are valid swaps, as the trim gauge is still in it's unopened Merc packaging.