BMW M57N / N2 Main relay and power loom DIY

Some of the looms we supply do not have the main relay and power feeds to the ECU. This is because the donor vehicle has this in a handy unit in the form of the ECU connector and the blue main relay in the ECU box with the wiring to and from both parts that is easily removed from the car. The main relay is also connected to the engine loom as well as that’s hwere it gets it’s activation signal from.
Some however may not have this unit. The drawings below are a wiring guide to create your own main relay loom using either a standard 30A vehicle relay or using the blue BMW main relay.
Please be mindful of your wire diameters as the ECU can draw a fairly high current whilst running.
From the battery, via the fuse to the main relay terminal 30 you require a 6mm² wire.
From the main relay terminal 87 to the joint where the wires are split into three to feed the ECU, you require a 6mm² wire.
From the joint wires are split into three to the ECU connector you need three 2.5mm² wires, one to pin 1, one to pin 3 and one to pin 5 on the ECU connector housing. These are supplied if you have bought the connetor housing from the webshop.
On the ground side, each ground pin (Pins 2, 4, and 6) requires a 2.5mm² wire to ground. These are supplied if you have bought the connetor housing from the webshop.
The brown wire which activates the relay is low current and a 0.5mm² diameter wire can be used. This goes to pin 44 on the ENGINE ECU loom connector
If using a standard relay the red wire between terminal 30 and terminal 85 on the relay is low current and 0.5mm² diameter wire can be used. If using the blue BMW Main relay, this connection is internal to the main relay and not required.