40 amp extra load - Power from where? (E39)

[RIL]

I'm about to add an extra electric device consuming some 40 A battery power continously. I'm placing the device in the front under the hood. The device will be relayed to ON on starting the engine. For this I have two questions:

1. Is there an existing preferred cable already in place which I could attach to (powering the 40 A relayed device), or will I have to add an extra 6 mm cable all the way from the battery in the back of the car to the front?

2. In order to control the 40A relay for the above device, it suffice if the extra device kicks in AFTER the engine is running fine (that is, avoiding extra load while the starter is working hard). Where from should I best pick up the 12V signal to the above 40A relay?

I'm not an expert on BMW so I would need helpt to locate any existing connection points.

I opened the Control Unit Box under the hood (to the right, near the front window) and I can there see a fairly "fat" realyed red cable, but I have no instructions /wire diagram available as to determine it's usage.

Regards from Sweden,

// RIL

[BBenedict]

There is an auxiliary positive terminal in the engine compartment of my 2002
540 for "jump" starting the engine. You could get your power there.

I don't have an answer for your second question.