How to put top up on 91 500 sl when switch does not work?

There is a special tool you have to buy (it costs about £30). The instructions are in the owners manual but not very good.

Before you do any of that, check the hydralic fluid reservoir, it is under the spare wheel in the back. All I needed to do in the end was top it up and it was all OK. Money and time wasted on the tool.