Background for those new to this. There has always been talk about not being able to retro fit cruise control onto an ///M. However in recent years a few Indy's have been successful in doing so. Last year I managed to obtain some info from a forum member who had it retrofitted at an Indy and had established that the connection in the ECU that needed to be connected was Pin 4 on plug X60002. The indy wasn't 100% with his comms to me so I need clarification as I didn't want to toast my ECU.
Recently another forum member was keen to get this fitted which spurred me on and with some confirmation on a few point from Scooba_Steve gave me the confidence to dig deeper.
1. Apart from the wire to the ECU, all the other requirements are the same for any other E85/6 that require the loom also to be fitted.
http://www.hutchison.org.uk/z4-forum/CC/CC_retrofit.pdf
I think even routing the wire thrugh to the ECU might be easier. By removing the top of the ECU cover lets light in and you can see a hole in he bottom going through the firewall. Remove the panel below the glovebox (2 screws) and then poke a piece of stiff wire down the hole in the ECU box. Tape the blue wire to the stiff wire under the glovebox and then pull it through into the ECU housing.
2. Connecting the blue wire to the ECU is probably easier than on any other E85/6. I'm including the following for completeness, but isn't required.
Pin 4 X6002 identified in this picture. This required removal and disconnection of ECU. Luckily you don't have to go anywhere near this. For clarity this wire is already fitted in the car.
Now the extra info Scooba_Steve posted mentioned about Pin 4 X6021 and said that he didn't think this went anywhere. So I managed to trace the wire from Pin 4 X6002 back to where I thought it went. I tested for continuity which confirmed this was the correct point.
I then removed the plug which confirmed suspicions that it didn't go anywhere.
So for the time being I used a Positap (Much better than Scotchlocks) to connect the CC loom wire to the wire in Pin 4 X6021
**This is where the wiring diagram says to connect the Cruise Control loom to **
https://www.posi-products.com/posiplug.html
I then fitted the Cruise Control Stalk using a dremel to remove the main section and file to get to finished size.
I then went on to do the final part which turned out to be the hardest. Only because it was like building a ship in a bottle as the loom for the LCM wasn't long enough to pull out of the dash, even after cutting it free from it's location. I used a descent ratchet crimp tool and wouldn't suggest using a cheap £1.00 job otherwise the connections won't be great.
Please ensure you cut the correct wires on the LCM. Best way to to extract the plugs from the connector and trace the wire from the pin locations. There are two yellow/purple coloured wires so be sure you cut the right one.
So all plugged back together and car was fine. The forum member who gave me the info last year reported he had to take his car back for coding as after fitting it didn't work. The Indy confirmed this and said the "Vehicle Order needed to be updated". Now I understand this to be nothing more than a list of options etc fitted to the car, and actually has nothing to do with them working or not.
So today I went to meet up with the South East Hooooooners and can confirm that Cruise Control is working 100%
I am going to hopefully find a correct male pin connector and re do the blue wire to give a OEM look by using the main block to connect into. I have an old O2 sensor so might canabilise that if the pin is the same size.
can others expect it to take less than your 2 years 
