Quote:
Originally Posted by trader4
What evidence do you have that it's wired that way? I don't have
a wiring diagram in front of me, but from the way the cables appear
to run, I would think the routing is:
alternator - starter - Terminal at top of engine compartment - battery
It wouldn't make any sense to run a whole separate wire all the way
back to the battery. And that wire would have to be about the same
current carrying capacity as the main one, because it would have to
carry the full load of jump starting the car. What would the purpose
be of doing it the way you suggest, instead of the simple, direct way?
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My evidence is basic 12V electrical theory.
A starter alone getting power will not make your car run. You can turn it over that way, but unless it's a < 1980s diesel you won't accomplish much more than that. Every other system needs to be energized as well.
Your main grounding point alone, is at the battery (not at the chassis like some people believe).
The jump start aspect under the hood is fine if you either have a slightly discharged battery, or have a lot of time to wait to charge up a severely dead one until they start wiring cars with zero resistance wiring and overcome voltage drop over distance.
The jump start terminal is there for convenience (because BMW likes to make batteries inconvenient to access--for several good theoretical reasons), not because it's a better connection.