Dragging up an old thread here, sorry! Just wanted to add a few comments I noted tonight that are additional to the excellent how-to by bandk.
I bought a Rover 45 steering wheel which was from a W regy, but bandk helped me identify the button age by the sticker I found on it, which gives the date of manufacture. The buttons I bought were the two button type but later Rovers got a three button unit which looks similar but with a mode button on the centre part.
The TF LE 500 steering is near enough identical to the earlier cars and in fact has PR3 embossed on the casting. However, digging around under the rubber I found two lug holes which were tapped already and made a convenient locating point for the base plate.
The wire and metal insert can be pushed out of the multi-plug with a small screwdriver and then inserted into your multiplug on your TF wheel.
Because of the age of my buttons I am having to get the adaptor kit coded PC99-X04 but if you get the later (post 2000 or 2002 in some cases) three button unit you will probably need PC99-X39. As the LE 500 has the Pioneer h/unit (DEH-6900iB) I need to get a PC99-PIO patch lead to plug into the back of the unit. Anglian Car Audio have been very helpful on Ebay in identifying what I need as has bandk, many thanks.
I will find out later this week if it works when I get my car back from the dealer where it is currently being resprayed, having the RPsensors done and the dash has been stripped for welding of the bodywork behind so it was a good opportunity to grab the steering wheel overnight.