There are 2 relays on the MKIII related to the fuel pump. The circuit opening relay is what actually turns the pump on or off. The Fuel pump control relay simply chooses how the +12V supply feed from the circuit opening relay will be routed, either through a resistor (+9V to the pump) or direct (+12V to the pump). Either way, if the fuel pump control relay is energized or not, there should still be power to the pump, the circuit opening relay on the other hand, is the decider on whether or not there will be any power at all.
Circuit opening relay = under dash, passenger side.
Fuel pump control relay = under hood, passenger side.
I heard that you should circumvent the fuel pump Control Relay (the one on the passenger strut tower) by cutting and connecting the 2 fat wires on the plug side to give a continuous 12V or 14V (?) feed. Apparently we have voltage modulation in the MK3 for the fuel pump to prevent overheating during idle or low fuel demand periods. Any thoughts on this? I am wondering if I should do it... I can see a reason to do it and a reason not to as well. If I dont do it, running at 21 psi, if I hit a low voltage situation to the fuel pump I will lean out. The Wideband doesnt prevent anything, it will just let me know I am running lean, but running lean at a high boost isn't ideal. If I do bypass it, I could burn out the pump from having it running full tilt all the time when its not needed.
Am I correct on this? (a little information can be very dangerous.. so I want to know from others who understand this)
(figured this was a relevant thread to post it in)