The first step is figuring out the wiring, this is fairly easy as the circuit board is exposed on the R-Sport cluster.  I used a couple of 6v batteries in series to provide 12v to the cluster.  Volvo is consistant in their wiring colors, red/blue is + and black is - the other wiring was figured out by folowing the  traces on the board, seeing which lights lit up with which wires, and plain old trial and error.  The low power output of the 2 6v batteries prevents any damage in case of a wrong hookup.  I numbered each wire for later identification. 
Then repeat the process with the stock dash, I wrote the numbers off the plug onto the back of the dash and drew a diagram to aid in identification of the wires.
The adaptor is next, I cut a template out of cardboard then transfered it onto the 1/16" aluminium plate.  it was cut out with a die grinder.  That's a 12" ruler next to it.
A local electronics shop provided some crimp on pins (1) to go on the end of the plug (2) that goes into the back of the R-Sport cluster.  The crescent plug got the same treatment.  One thing I found out the hard way is there is a red wire (#6 on my '85)  that needs power from the instruments to power the AC delay relay.  I had to provide power from a fuse before my AC would work.
A rough idea of what it looks like from the drivers seat.  After this picture was taken I switched the gauges on the right around.  I now have Boost, Oil Temp, Ambient Air Temp and Fuel/Air on top with the clock in the single space on the bottom.  One of the nice things about the R-Sport cluster is it frees up the two holes taken up by the oil and volt gauge.  Speaking of oil pressure, the R-Sport oil gauge works with the 5 bar sender but it reads double the pressure (it's a 10 bar gauge)  the oil light wire was hooked up to the EGR light just to be safe.
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This is a great adition to any '81-'85 Volvo.  Complete instructions are beyond the scope of this page, for one thing there were many different R-Sport clusters made, all 4 that I have run across have had different wiring.  Also not all 240s are wired the same.  Best advice is aproach it slowly and use common sense.  Red and Blue/Red cary + Black is a safe bet to be a ground, (may ground to a sensor)  A multi-meter and a good wiring diagram are your friends.   The turn signal wires (a green and a blue) that operated the 2 independant lights on my '85 worked perfectly hooked up to the green and blue wires to the single light on the R-Sport gauges.   If you take it one wire at a time you can get all the lights and gauges working like they were factory installed.