| Most people are aware of the fact that at some point in time through your upgrade path you will need to upgrade your fuel system to a more robust configuration that is capable of delivering an ample quantity of fuel to keep up with the airflow capacity of the engine. There are a lot of options out there ranging from a dual stock pump installation all the way up to very expensive high-performance pumps (like aeromotive's setup). Each of the options will present their own challenges to successfully pull it off as each of them will require varying types of components. I want to specifically address the use of a dual-pump setup (as opposed to a large, single pump config like the aeromotive systems) as it presents some interesting electrical, mechanical, and fitment issues. At the moment I have Dee Ridgeway's fuel tank bulkhead, both Walbro pumps, and a couple of fuel controllers. My primary focus at the moment is the fact that when this setup was originally installed, we wired both pumps in parallel and supplied power to them through 1 fuel pump controller. The car ran great for about 50 miles before the engine began stumbling and the pungent smell of burning electronics filled the cabin of the car. I was afraid of this happening when we installed everything, but we were working from a set of insrtuctions that were supplied to us that stated it could be done. I have disassembled the TT and NA fuel pump controller this AM to take a closer look at their construction. I have come across some very interesting differences. The pump on the left is the burned up TT controller and the one on the right is the non-turbo controller. The JECS part number is the same and all circuits are identical between the two controllers. The only difference found are the resistor banks - the common resistor banks use different resistors and the TT has an extra set of resistors that the NA does not have. According to the FSM, (EF&EC-26), the twinturbo has a 3-speed fuel pump controller and the NA has a 2-speed controller. The main difference is the mid-load pump speed: TT
IDLE: 6V
MID-LOAD: 7V
HIGH-LOAD: 12V (battery voltage) NA
IDLE: 8V
MID-LOAD: 12V(battery voltage)
HIGH-LOAD: 12V(battery voltage) A few weeks back, Roland (DAYTONAZ) brought his car over so we could test-fit the eXtreme intake on his TT and I noted that his fuel pressure at idle was 40psi; it should have been around 35psi. You could also hear the fuel pump just buzzing away at idle too. His fuel system was still OEM, so this was peculiar. I checked a few things but came up with nothing, but I handed him a non-turbo pump controller to try out as it seemed like his controller was having a problem. He contacted me a few days later to tell me that he put the NA controller in there and the fuel pressure dropped down to 35psi at idle and the pump quit buzzing. He opened up his TT controller to find that some circuits had burned up - this was causing the pump to just run at full speed all the time which was consistent with the fuel pressure we were noting at idle prior to the controller swap. But he also noted that there was a sharp spike in pressure around 3/4 throttle with the NA controller in there. Now that we had discovered the problem, he got his hands on a good working TT controller and upon installation, he noted that the pressure at idle was a correct 35psi, but it no longer had that hard spike as he rolled into the throttle while driving. This is obviously all consistent with how the fuel pump controllers work and the differences in pump voltage between the NA and TT setups. 
Something of interest to me, of which I have never looked into before, is the ECUs control sequence for the multi-speed pump operation. The ECU connects to the fuel pump controller to control its pump voltage output. There are differences in the NA and TT ECU wiring harness as there is an additional control line on the TT model ECU harness that the NA does not have (EF&EC-156). After inspecting the voltage outputs of these control lines with the engine under varying amounts of load I found the following: (performed on a native TT vehicle) Pin 104: (Black/purple)
Idle and light load: 1.8V
Mid load: 5.0V
High Load: 5.0V Pin 35: (Purple)
Idle and light load: 1.8V
Mid load: 1.8V
High Load: 5.0V With this information, it appears that pin 35, which is only on the turbo model harness, only goes to 5.0V at high load. The varying pump speeds ARE important. Many have found that after upgrading their fuel systems, they cannot get their fuel pressure down to the 35psi at idle that it should be at, and despite their attempts to turn the regulator all the way down or to replace it alltogehter, the fuel pressure is still too high at idle. What is happening in these cases is they are simply overrunning the regulator - the regulator cannot bypass enough fuel to lower the rail pressure any further AND/OR the return line is insufficient to carry the volume of return fuel, resulting in uncontrollably higher rail pressures. Without the varying pump voltage (which directly controls the pumps output), you WILL overrun the regulator and return line's capability. For this fact, it is vital that the 3-speed control is maintained when upgrading the fuel system in order to properly and smoothly control fuel pressures. On the same token, you would not want to use an NA EFI harness in a TT as it will be missing this additional line to the controller. So, with all of this in mind, it appears that we have some confinements with regards to part usage. However, it also appears that the non-turbo fuel pump controller can be easily changed to a twinturbo fuel pump controller by simply changing two resistors and adding two others. Total cost is about $2 and a little bit of time with a soldering iron. Although this is a very simple modification, it will require that a twinturbo ECU and twinturbo harness is used in order to take advantage of the 3-speed control of the TT setup. Now, the problem that one will run into is the fact that trying to drive two fuel pumps will require more current, of which it is apparent that the stock fuel pump controller will not handle. The solution? Buy a second controller (you can use either a TT or modified NA for this) and about 12" of the harness connector. You can splice the second harness into the original to connect the second controller, and then run additional power lines to the second fuel pump from the extra harness connector's pump power terminals. The benefits of maintaining the 3-speed pump control are great and the cost of buying two walbro pumps, an extra pump controller, and a pump controller connector with about 12" of wires on it will be significantly less expensive. With this setup you will not have any regulator/return line overrun and will be capable of flowing more fuel than you'll probably ever use. In the next few days I will be re-constructing Dee's dual pump setup. I didn't have all the equipment I really wanted to use when I originally installed it a few weeks ago when I was up in PA so I'll be refining the fabrication and posting some good pictures and diagrams of how everything hooks up both mechanically and electrically. Sorry for the long post, a lot of it has been just my thoughts and findings through the day as I've progressed with the research - admittedly a long winded round-about post, but just wanted to share. I believe this setup will be the ideal method of upgrade for any TT, at least, I wont stop until it is. :)
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Dual Fuel Pump Setup. >>>> Just a prelim-- - 
