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First time power supply build

Practical Harness Construction - Club Level

Discussion and questions related to the course Practical Harness Construction - Club Level


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Hi guys, just wanted someone to check over my diagram for my first wiring job and let me know if there are any mistakes. My other queries were:

1. Does the fuel pump relay terminal 85 need to be grounded by the ECU? I have just copied what I have seen from the practical harness course and a couple of other diagrams. I am guessing the ECU to 85 on the relay is necessary only for returnless fuel systems, or am I missing something? If it is a return style fuel system, can I just terminate the relay to ground?

2. I have installed an ethanol content sensor quite close to the fuel pump, is it ok for me to run 12v supply to this through the same relay as the fuel pump?

3. I have an aftermarket dual fan setup for my radiator, I dont have a clue how much current they will draw (dual 12" fans) I would like to be able to control these off just one relay, how could I do this? If advised otherwise, I will go ahead with one relay per fan as drawn in diagram. The reason I would like to use one relay is I am running out of space!

Any guidance is appreciated :)

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1. Regardless if you have a return hose from the fuel rail, it is normal for the ECU to control the fuel pump relay. The reason is that the ECU will turn off the fuel pump if the engine stops rotating (which can be a safety thing).

2. I would say yes, as a sensor will not draw as much current as the pump.

3. Just find how much current the fans are ratted at and do some addition. If the fans are rated in power, you can calculate the current easy. (Power = V*I) Make sure the fan wires are also rated for your current draw, maybe 14awg.

The wiring diagram looks good to me.

n addition to Jonathans reply - not worth to mention about:

1. When you will switch ignition to ON position and not starting your engine, your fuel pump will shut off by ECU after couple second. It is really annoying sometimes to listen for a working fuel pump, especially if it is large and noisy like Bosch 044 pump :)

3. Better to control each fan individually as it will reduce load to alternator and engine.

if you have room and can do it safely you can spin up your fans on the bench\floor using a car or drill battery and use a multimeter to see how many amps they draw. My fans said how many Watts they were on a sticker and I could use a calculator to determine the amps.