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My first standalone wiring harness

EFI Wiring Fundamentals

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Hello, I'm from czech republic, my name is George (Jirka in czech) and iam in my first project. Iam building hillclimb and drift car. It is BMW E36 powered by M50B25 non-vanos.

I want to run it on ECU MASTER EMU CLASSIC and iam designig my first standalone wiring harness in my entire life and iam quiet lost in the most important part of it- power supply. So...i prepaired basic diagram of it. Can you tell me what is wrong and how to do it correctly? (Relay pinout and fuses are not included in this diagram. )

I hope, U will help me (lead me to) construct my first functional club level wiring harness.

Attached Files

G'day Jiří.

A couple of things:

I don't see any fuses in your diagram? They're really essential and should absolutely be used.

Your relays seem to be missing a wire? Relays have two circuits inside them, the switching coil, and the power circuit. The ECU controls the switching coil, which turns on the power circuit. This means you usually supply the power circuit of each of your relays from the battery, (via a fuse!), whereas the supply to the switching coil may be from another location. Hopefully this image from our club level harness construction course will help:

In that image, the relay switching coils are triggered by the OEM ignition barrel, like you are wanting to do with your setup. Something you will need to test is that the OEM ignition barrel in your vehicle continues to supply 12V on the accessory output when the barrel is turned to the 'start' position. Many vehicles disable the accessory output while the engine starter is being cranked. Does the OEM radio turn off when the starter motor is engaged? This is why in the image the 'Enable' circuit is controlled by the 'On' circuit, so they will both always be on or off at the same time, never independent of one another. Its a compromise that had to be made for this particular design.

The oxygen sensor heater circuit typically draws around an amp, so doesn't need to have its own relay, typically it is supplied from the enable relay.