Originally Posted by CLightning
Ali SC3, this is my current setup which is similar to your diagram (I think). Please excuse my novicity in regards to relays, but I'm still having a hard time understanding how placing the switch between the relay(85) and the ground compared to placing a switch between the relay(86) and a +12V ignition source would make any difference? Thanks.
Hey Mike, your diagram may look similar but its wired in non conventional way.
Relays take some getting used to so I can help you work through it.
The way you have it connected now, the fuel pump is supplied power by the fuel pump ecu (9v low and 12v high speed operation) when the kill switch is on. Also your kill switch is on the power side.
The reason to put the kill switch on the ground side of the relay, is that its isolated by the relay then and some "switches" introduce alot of noise into an electrical system when they open and close like for example a rocker switch, sort of depends on the design and quality. the speed of the switch opening and closing and other factors affects how much they mess with the electrical system. You can guess that there are lots of sensitive components on your ignition line, and when you flip that switch you are affecting them essentially. When you put the switch on the ground side, you are letting the relay do its job by switching the power off much better than a rocker switch can.
Also if you had it on the plus side, and it somehow managed to ever touch a ground which in a switch is a possibility if it touches something or where its mounted, you would short the entire ignition system connected like that and blow the fuses at the least. if you grounded out a switch on the ground side, well the fuel pump would just turn on.
The other change I mentioned is that the fuel pump ecu is what you use to turn the relay on with pin 86, in your diagram you have the ignition power doing it, which means your relay is on as long as the car is on and the kill switch isn't on. since the fuel pump ecu is still supplying the pump with power when the relay is on, you keep the safety features of the fuel pump ecu even though you have it wired oddly. its odd because the relay is energized but the power source is not always live (fuel pump ecu only outputs power when it sees engine rpm's). since you generally want the relay on when the power is going to go through it, its not the conventional way to do it.
now lets take it another step, you want 12V all the time so you remove the fuel pump ecu line and connect a battery line. now the fuel pump is on whenever the ignition is on and the rocker is on and you just lost the ecu safety function = not good. the answer is to just use the fuel pump power wire for 86 instead of the ignition power, and then no matter what you use to supply the fuel pump power, you have all the safety functions of the fuel ecu (cause fuel ecu controls relay now), and you place the cut off on the ground side.
lets say you don't want 12V all the time, you can just use the fuel pump ecu wire to power the fuel pump, and power the relay on 86. you put the rcker switch on the ground side and this allow you to turn it on and off, and you get normal fuel ecu to fuel pump.
so to summarize:
fuel pump ecu wire on 86
ground with inline kill switch on 85
30 is the power source, you can use the fuel pump ecu wire again or if you want 12V all the time run a proper gauge cable from the battery.
87 goes directly to the fuel pump.
That is how I would wire it anyways. also you dont want a kill switch bypass on the plus side for the same reasons mentioned above (unless you only operte it when power is off and have it mounted in a place the terminals can never touch ground). the kill switch does the exact same function when wired right (turn pump on or off), the bypass switch is redundant and risky as there is no ground side on the power side of the circuit to do the bypassing on. you only want/need the 1 kill switch IMO but that is enough info to get you started. look around on the net lots of diagrams for switch on the ground side of the relay as it is the proper way to hook it up.