What makes them so much more desirable than the simple idiot lights
Mick,
Just saw this post. As far as I'm concerned, what makes them desirable is that the gauge set (Ammeter and Oil Pressure guages, with idiot light for water temperature) will tell you things have gone wrong BEFORE absolute disaster strikes - e.g. the idiot oil pressure light will come on when the oil pressure falls below a certain point (I think it's 4 psi). If your oil pressure is down to 5psi when you're doing 50mph you've got big problems if you don't know - and the red light isn't on yet (why else do they call them "idiot" lights??). So what makes them desirable is they fit into the dash (not nailed on underneath) and they look the real part (even if they are a non-genuine, after-market accessory). Personal experience over a lot of years tells me I want to see oil pressure & water temp, but the pre- FB model cylinder heads didn't have a vacant port into which a temp sender could be screwed - I assume that's why it's oil & amps and not oil and temp.
Martin