Over the past few months I’ve noticed the oil pressure LED getting dimmer after the initial dashboard power-on-self-test has finished. Then a couple of weeks ago, no oil light at all. If I pulled the electrical connector off the switch and shorted it to the crankcase, the lamp worked fine, so the oil pressure switch was u/s, fubar, stuffed ……….
I bought a new one from Ultimate Parts in the UK that came in a plain zip bag, not an Aprilia one and isn’t the same as the original – requiring a 24mm socket instead of the 
original 21mm. As such I have a sneaking feeling this is an aftermarket part and not genuine – but sold at a genuine price! Either way, both new and old are marked as 0.3-0.6bar (4.35-8.7psi).
Swapping it out on the Rally-Raid was a simple 5 minute job – remove the aluminium sump plate, disconnect the electrical connector and use a deep 21mm socket on a short extension to clear the sump guard frame and unscrew the old unit. You’ll lose a couple of tea-spoons of oil but that’s all. Simply swap to the 24mm socket to fit the new one, reattach the connector and refit the sump plate – job done. The job’s made all the easier if you do it on the side-stand rather that the main stand as the switch is mounted on the right hand side of the engine!