Engine Conversion Wiring

Wiring up a BMW engine can be a daunting task whether that be an M47 or any of the M57 range.

In terms of getting the engine running, it doesn’t really matter what you’re fitting it into, the principles are all the same. Over the past years we have provided parts for M57 conversions into thousands of vehicles! Some of those include:

  • Land Rover Defender (This is currently the most popular swap)
  • Land Rover Discovery 
  • Ford Transit Mk6, Mk7 and Mk8
  • Ford Sierra
  • Mitsubishi Shogun/Pajero
  • Nissan Patrol
  •  Log splitter
  • Hover craft
  • Numerous boats

There are probably more that we don’t know about, the length of the list is only limited by your imagination.

To help you on your way, below we will discuss Body side and Engine side wiring. Both of these strands of wiring are joined together at the ECU.


Body side

As the name suggests, this is the part of the wiring which goes into the body of either the donor BMW or the recipient of the engine. It includes the OBD port, throttle pedal, ignition feed and some other outputs. Essentially this is the wiring which links the operator or driver to the ECU.

The body side is where our standalone looms come in. Quite often our customers buy just engines. If you have a donor car and confident with wiring then it is possible to make your own body side wiring but in our experience the time taken far outweighs the cost of our looms.

The looms that we currently stock are:

These come with their own installation instructions which can be found at the bottom of the product desicription.

     Main relay 

One of the most critical wiring aspects of your engine conversion wiring is the main relay. The purpose of this relay is to switch power to the ECU, the relay itself is controlled by the ECU. Essentially, the ECU decides when to power itself and when not to. It is important that this logic is retained in your wiring setup.

When you turn the ignition on, the main relay should turn on.

When you turn the ignition off, the main relay will turn off after approximately 20-30 seconds. It is important that you do not turn off or remove power from the ECU before the main relay has turned off. This includes battery isolators, disconnecting a battery, etc. Failure to follow this rule will probably end up in your EWS emulator coming out of sync.

When it comes to wiring up the electric pre-supply pump, you can either have it ECU controlled or just run it from an ignition feed. Running from an ignition feed can often be simpler and is one less point of failure; you know that when your ignition is on then your pump should be running. When ECU controlled it will turn off automatically after 30 seconds if the engine is not started.

On DDE 4 ECUs the main relay loom is usually separate from the engine harness. Automatic models may have a main DDE relay loom integrated to the engine harness. In any case, you can check that the relay is connected to plug 1 in this configuration. This will enable the ECU to control its own power. 

Engine Conversion Wiring House of Torque

DDE 5 main relay (Follow the instructions at the bottom of the page)

Engine Conversion Wiring House of Torque

CAN – bus 

In some cases you will need to wire up a can bus circuit, for example you must ensure the can bus circuit is correct when using an automatic transmission.

CAN Hi wires should be connected together.

CAN Lo wires should be connected together.

One thing you must check, with all power turned off, the resistance between CAN Lo and CAN Hi should be 60 ohms.

If the reading is 120 Ohms, you should add a single 120 Ohm resistor from CAN Lo to CAN Hi.

If the reading is very high (thousands of Ohms), you should add 2x 120 ohm resistors.

Ideally you should add the resistors at the extremities of the circuit. However in reality, since the CAN circuit is likely to be short, it won’t really matter where you put the resistors.

Engine Conversion Wiring House of Torque

Engine side

Engine side is the wiring that controlls all sensors on the engine, the injectors, and in most cases the power into the ECU. 

It is possible to find all of the BMW wiring diagrams online but they are a very dry read! We have spent quite a few hours reading and extracting the relevant information so that you don’t have to.

The following rules apply in nearly all cases when it comes to the M57 engine harnesses.

  • Power travels from the battery, through the main relay and then to the ECU. It is important that this is respected and that the ECU isn’t connected directly to the battery. (See the body side fitting instructions for more information)
  • Brown – Ground
  • Green – Ignition feed
  • Red/White – Power from the main relay
  • Red/Blue – Power from the battery into the main relay
  • Thick black – Starter motor trigger

We have put together the following infographics which cover almost all of the engines:

Engine Conversion Wiring House of Torque

E53 M57N

Iron block engines found in the E53 X5. E60 iron block engines will also look very similar

Engine Conversion Wiring House of Torque

E60 M57N2

Alloy block engines found in the E60 or E60 LCI

Engine Conversion Wiring House of Torque

E70 M57N2

Alloy block engines found in the E70 X5

If the engine you are wiring doesn’t match exactly with the diagrams above, don’t panic. Just remember that they all follow the same principles. In most cases the wire colours will match even if the plugs don’t.