Hello everybody! This is my first post here, though I've been lurking a lot over the past months gathering info on how to install my 7970 safely in my Mac Pro 5,1. I noticed that though many people have posted their setups, I couldn't find a thorough, complete how-to guide on how exactly to do this and what exact parts to get, so after successfully completing my build, I figured this should be my first post. Before starting, just wanted to give a thank-you to all those whose posts have helped me or inspired my build, especially Dr. Stealth, OrangeSVTguy, and J-MI. Also, do everything at your own risk; if you don't know what you're doing, it might be a better idea to use the drill. As always, I take no responsibility whatsoever for any burns, dead Mac Pros, raging, screaming, crying, frustration, failing, confusion, dead kittens, etc. With that done, lets get started! First, the supplies youll need (the ones I used are in parentheses): Basic stuff: A Mac Pro 2009, 2010, or 2012 [sic] A GPU requiring >= 225W (Sapphire 7970 OC w/boost for me) Auxiliary 5.25 drive bay PSU (ePower EP-450CD 450W) A copy of the Mac Pro Service Manual: (http://tim.id.au/laptops/apple/macpro/macpro_mid2010.pdf) #1 Phillips screwdriver 2.5 mm hex driver Pliers Electrical: Soldering iron/ station Solder (Rosin Core) Wire strippers (should handle 18 gauge wire) 18 gauge hookup wire (solid wire) #8 size Ring tongue terminal 3/32 or 3 mm Heat shrink Electrical tape Cables: SATA male to 4 pin molex female cable 4 pin Molex male to molex female extension (2 of these) Unsleeved 8 pin EPS male to EPS female extension Zip ties or velcro cable straps Strongly Recommended: Anti-static wrist strap Multimeter Pin Extractor capable of extracting EPS pins With all the supplies, the first step is of course to open up the Mac Pro and remove the hard drive sleds, the optical drive bay, and the main PSU as detailed in the service manual. After this, your Mac Pro looks like this. Next, either cut the EPS extension cables down the middle or extract the pins from the female connector. If you cut the cable, strip the ends of all wires where they are cut. There are two gaps between the front of the Mac Pro and the plate supporting the optical drive; thread one set of cables through the gap in front, and one set of cables through the gap in back, as shown in below image. Make sure the male connector is where the optical drive was. Now, slide the auxiliary PSU into the space below the optical drive. Take its power cable, cut its plug off, and strip off the sleeving and then the ends of the wires as shown. Note which cable goes to hot/line, which goes to neutral, and which goes to ground in the AC outlet. This can be found using the multimeter to check continuity between different color wires and prongs of the plug. Finally, plug the Aux PSUs power cable into the aux PSU, and route the cable out the back of the assembly through the space between the aux PSU and the optical drive. Also plug the molex to molex extension cable into the aux PSU. The final setup is below. Now, take the main PSU and remove all the screws that are on its exterior. Also, there is a felt lining around the white AC cable receptacle; pull this off as well. Now, remove the side plate from the PSU; note that there is a cable now visible which goes from the top half of the PSU to the bottom half. Next, pull the top and bottom halves of the PSU apart, and lay the top half down and the bottom half on its side. Take care to disconnect the cable which was seen earlier as you pull the PSU apart. You may also have to cut part of the thin plastic plate that goes between the top and bottom halves. After this, the PSU should look as shown below. As shown in the above picture, unscrew the five screws depicted, and also unplug this connector on the top right in the picture. Also unplug the screw on the bottom of the PSU which holds down the ground wire. When this is complete, lift the green circuit board off of the aluminum housing, flip it, and set it on top of the top half of the PSU as shown below. Now for the fun part. Were going to draw the AC power for the auxiliary PSU straight from the main PSU, off of the 120V/220V leads. For this, take a an 18 inch piece of hookup wire, and strip the ends. Now, note the two little nubs sticking out shown in the below picture. One goes to the hot/line prong of the AC plug, while the other goes to neutral. Take the stripped end of the wire, curl it into a loop, and put it around one of them; note whether this cable is hot/line or neutral (I just used a black cable to signify neutral and a red cable to signify hot). Now, solder the loop onto the little protrusion, and do the same with another piece of wire and the other protrusion. The final setup should look like is shown below. Keep in mind which wire is hot and which is neutral. Also, if you have one, use the multimeter to test continuity from the hot and neutral prongs of the white AC plug and the free ends of your soldered wires. Now, close the main PSU back up, just following the reverse of the steps used to disassemble it and making sure to screw the ground wire back in, and reconnecting all the cables that had been disconnected. Thread the two new wires out alongside the other cables that come out from the PSU. Also, use the pliers to twist off the small square piece of aluminum depicted below; otherwise, it could cut into your wires. I had to eventually do this. With all this done, put the main PSU back into the Mac Pro and thread the new cables alongside the main power cables to the place where the optical drive goes. Screw the main PSU back into place. Plug the main power cables back in. The setup now looks like this. Now, concentrate back on the EPS extension cables. With the free ends of the wires on the same side as the GPU, we need to reattach the female connector to these wires. If you used a pin extractor, simply reassemble the connector. Otherwise, solder the appropriate wires together here, as depicted below. I soldered since I didnt have a pin extractor and I couldnt get the staple trick to work (killed a cable trying), but if possible pin extraction is a better option. My cables were color coded, so it was easy to see which two cables to solder together. With this complete, now take the hot/line wire that was soldered onto the main PSU, and the hot/line wire from the auxiliary PSU power cord, and solder their free ends together. Do the same with the neutral wires from the aux PSU and the main PSU. For the ground wire, attach the ring terminal to its end and crimp it with a crimping tool, if you have one, otherwise pliers and electrical tape should suffice. Unscrew one of the screws holding the main PSU fan down, and screw the ring terminal down under it as shown below. Now, we can test the setup. Attach the SATA to molex adaptor to the bottom SATA port on the optical drive SATA cable, and attach the molex end to the extension cable coming from the auxiliary PSU. Attach the EPS to 6+2 pin cables between the auxiliary PSU and the existing GPU (a 5870 in my case), and now just leave it all open, plug the Mac in, and turn it on. If all this worked, its time to close it all up. Shove as much of the aux PSU power cord as you can into the space between the optical drive and the aux PSU. Also, I pushed the SATA to molex and molex extension cables through the space on the side of the drive bay enclosure, as shown below. Then carefully, making sure that there are no cables in the way, slide the entire enclosure into its place in the Mac Pro, plugging in the EPS cables to the aux PSU as you go. Now just attach the EPS to 6+2 pin cables to the EPS female connectors from the extension cables, and bunch up the cables with zip ties or velcro cable straps. Reinstall the hard drive. If you want, test the entire setup with the old GPU again. Finally, install the new GPU as detailed in the service source, plug it into the 6+2 pin cables, plug it in, and turn it on. Wait a few seconds (remember, no EFI yet, so no boot screen), hold your breath, and then SUCCESS! Assuming you did everything correctly, it should all work now! Well, this all was quite a project, but its been going for two weeks now, and has handled whatever Ive thrown at it, so it all seems to be working well. Hopefully this guide will help someone else find all the exact supplies and preparation required before they embark on the same project I did.