When installing ECU with Motronic88 connector to the BMW M52 harness, verify the following:

ECU Unplugged

* mot88/73 is connected to main relay control pin (DVM connectivity test)

* main relay resistance = ... Ohm (fill this in, should be between 75..150 Ohm)

Ignition off:

* main relay is NOT powered

Ignition on:

* DVM DC voltage mode (+12V as a base):

** main relay control pin (same as mot88/73 verified before) measures appr -12V (if DVM black is connected to +12V).

* This mean that main relay is powered by the ECU (actually EC36/16 (p259/ch1) output, configured via MISC1 output function "always ON")

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Main relay not switching ON when ECU powered, possible causes

* main relay coil not getting +12V (can be rectified locally)

* or ECU does not pull down the mot88/73

** (most likely configuration, can be rectified locally)

** or something else

* Main relay contact problem (can be rectified locally)

* Main relay faulty (can be rectified locally)

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Check config

Download [.vemscfg] and compare.

* capture a short vemslog, and publish on your MembersPage

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Ignition ON: (test example)

* VT is CONNECTED

* main relay is powered (0.08A)

** mot88/73 is pulled to GND via (EC36/16 = p259/ch1)

** actually configured via MISC1 output function.

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If ignition is OFF (ECU does not get +12V power via M52/49=EC36/25 supply), then

* VT is disconnected

* main relay is off (0.00A)

** even though ECU is plugged in and harness is powered

** so it's not just some wire inside the ECU, main relay control pin mot88/73 is only pulled to GND when ECU is powered by ignition ON.