There are three or four small screws that need to be removed before the back piece comes off and reveals the many bulbs that lie beneath it. Having removed this gauge recently, I do not think that it would be practical to remove this piece without first removing the whole gauge. If it is possible, it would probably be a lot more tedious than dealing with the oil capillary and the temperature gauge line, neither of which is really difficult so long as you take your time and are gentle with everything.