bmw M42 main relay issue control

[Petros30]

Hello everyone,

I'm new to this forum ,is the second time that I install a link ECU, first it was to my university project which you give to us a link G4+ ATOM like sponsorship for Tyφοοn Motoracing Team. After that I buy a Monsoon for my personal car bmw e30 m42 but the wiring now is a little more difficult.

My problem is the wiring of main relay because the Motronic 1.7 send a ground to pin 85 (27) of main relay which have supply from ignition switch input (56). Also the OEM ecu have an input from pin 87( main relay)(54) and a battery voltage input (26). (there is attached image)

My first thought was to use one more relay to use the ignition switch(56) to give ground to 85 main relay (27). And take +12V for monsoon from pin 87 main relay(54). After that I find to forum a diagram that use a Mosfet transistor and a diode to do exactly the same job. although, I do not understand why he use diode to connect the to side of relay 85 and 86 (image )

There is other solution to my problem and what do you suggest? thanks you for your time!

Peter MS

[Simon]

Either option would work well Relay or transistor

Attached image is the circuit we use on some of our plugins.

The ECU power is then from the main relay.

 

Edited January 11, 2017 by Simon

[Petros30]

Thanks you very much for your replay, if you can explain what is SMAZIO-13-F and it not nessesary to use any diode?

 Thanks again Peter MS

[Simon]

The SMAZIO is a diode but it from another part of the circuit board I grabbed the image off.

On this circuit the transistor has an inbuilt diode for protection. So no external one required.