Bcm - Whats In The Box

[Dieseldonkey]

Looking to be educated here.

Retro fitted some fog lights to the van at the weekend. Thanks to @Pauly for the kit and @zebra for his excellent write up on how to do it.

Part of the process involved getting access to the BCM and its connector blocks (If I have to access that thing ever again, it will be too soon) .

However got me thinking. There seems to be no relays in the circuit to switch on the fog lights. I noticed the pins on the BCM vary in thickness, so I presume some of the circuits within can handle higher currents than other. I'm also guessing one connector does the input and the other the outputs?

Is there any kind of relay built into the BCM or is some sort of solid state transistor able to handle the current involved in supplying 55 watt bulbs?

 

[Loz]

The "Relays" are electronic versions. you supply it with various fused inputs of various sizes appropriate to the circuit in question then there a number inputs from stitches etc and a number of outputs.
Then there is a micro-controller inside that controls the switching based on some programming.

 

[Pauly]

It’s quite a box of tricks the BCM, as @Loz says there’s plenty going on inside, lots of the terminals are fixed and carry out a set job like the foglights you connected you feed a set terminal from the fusebox and this is sent out of another set terminal when active and is controlled by inputting to another set terminal, many of these ‘relay’ type terminals are fixed to do a set job but there are also plenty of programmable terminals on there as well for example one of the pins on the BCM is used to send an output to one (only one) of the LED headlights if you have them installed but if you have barn doors that same terminal is used to control the deadlock on the back door and the LED headlight wires are doubled up in another terminal, these types of terminals are controlled by the firmware in the BCM if the function is set or via the programming (read coding/adaptions) if its variable/optional

 

[Dieseldonkey]

Thank you chaps. Very informative. That's enhanced my understanding somewhat. It just felt odd holding a little box of electronics, yet knowing it's dealing with considerably more than milliamp input/outputs.