Ok, so I have quite a complicated fuel system that needs some tweaking. I have a Walbro 460 in tank, a 3L surge tank, a large 42401 Fuelab external pump and a 52901 Fuelab FPR. Now I went with these units because my ECU (nistune) does not have capability to control a pump. This pair of pump and reg are made to work together in that the regulator has a PWM output that connects to the pump speed control terminal. The catch is that the manufacturer specifies that the return doesn't go to a (non vented) surge tank, so mine was plumbed back to the main tank. I was expecting that the walbro would fill the surge fast enough to give me some headroom at low load to keep the surge full ready for high load. This caused some issues for me where the external was draining the surge tank. So the work around for me as I see, is to change the plumbing so that the rail return goes to the surge tank, keeping it full, but then I still need a way to control the external pump speed as it is not recommended to run constant full duty. Now, back to the pump speed control... This terminal can take either a PWM or a 0-5v. Also, if this terminal is left open the pump is perma full speed, and it it is earth the pump is perma slow speed (not so slow at about 500+L/hr so I found out). Voltage method of control, <0.25V is low speed and >2.5V is high speed. I need some way of switching the pump automaticlly as I don't want to have to manually toggle it. Option 1 as I see is to switch high/low based on boost or fuel pressure with something like a hobbs switch and a relay (either earthing out or opening the speed control terminal). Option 2 is connecting some feedback from the ECU in 0-5v format directly, along the lines of TPS or MAF where low V equals low load and high V equals high load. Unfortunately TPS or MAF voltage scales don't really fit the low 'cruise' V requirement as idle TPS is 0.45ishV and MAF is ~1.3V. The first option seems pretty straight forward. The second option tho, are there are any other options that I have overlooked??? Discuss please.