Not long after I'd bought my Amazon I was reversing while a car was in front of me. I had no lights on. Completely by chance I noticed via the reflection of my Amazon in the other car that the small front lights (parking lights?) started to light whenever I hit the brakes!

That meant there was a short circuit between two normally separate circuits. I started by checking the rear lights and found out that the previous owner had put a single spiralled 21 W bulb in place of the left brake/rear light which uses the 21/5W double spiralled bulb (the European version of the rear lights is amber/red/white, with three bulbs per side, respectively 21 - 21/5 - 21 Watts). The single contact of the 21 W bulb bridged (short circuited) the double contacts for the brake/rear lights. Short circuit found.

I think that the parking lights and instrument lighting are on the same circuit, because when the parking lights are on, the instrument lights are also on. What I'd do is apply the brakes and check if the (front) parking lights also light. If that's the case, start looking at the bulbs in the rear lights.
You can also check by turning the lights on and look at the rear lights. Normally the rear lights are 5 W (the brakes are 21 W). If there is a 21 W bulb in place of the 21/5W it will, of course, be brighter than the other one.