Not knowing much about the BMW systems I can give you a rule of thumb (old
English law for keeping the wife in order) of starter motor wiring.
Usually there are 2 large 8mm studs one has a heavy wire attached going to the
actual motor windings and the other should have the heavy wire from the Battery
connected to it. this cylindrical THING is called the Solenoid (you might have
another name for it.
There are usually 2 other smaller spade connectors at 90deg to the heavy
terminals one is for the connection to the ignition key so when you turn to the
start position the power is routed to the solenoid and this does 2 jobs at once
(like the wife) 1 - it initiates an electro magnet that pushes a fork that
pushes a gear connected to the shaft into mesh with the flywheel and 2 - it
connects the two heavy wire connectors together to route the batter power
(300+Amp) to the motor windings and hopefully, the motor turns and the engine
The, usually smaller, other small spade connector used to be used to increase
the voltage available at the coil (older cars) to compensate for the voltage
drop when the starter is drawing it's 300 Amps. this was commonly called a
"cold start" system and initiated by FORD in the 1960s (here in the UK anyway).
However, with the advent of massive electronics and fuel injection this may not
be used anymore.
Sir Hugh of Bognor
The difference between men and boys is the price of their toys.
Intelligence is not knowing the answer but knowing where and how to find it!
Bognor Regis, W.Sussex, England, UK
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