And this is where the problems can start.
My main role at Toyota/Lexus was as a prep tech which meant I fitted all the genuine accessories (tow bars, sat nav, parking sensors, stereo upgrades and basically anything that’s an optional extra) and these need to be plumbed into the wiring looms correctly, and by that I mean fitted as it would be at the factory.
This in turn means, dashboards out, carpets out, seats out etc so I could get at various loom plugs to pin in the wiring needed, which is extremely labour intensive.
The problem with non gen accessories is that when fitted the wiring is hacked into the looms via solder (bad) or scotch locks (fucking terrible) and this in turn can play havoc with the can bus system.
ECU’s (the most basic cars will have 30+ of them) are required to see certain voltages and certain systems run on different voltages, so when someone starts adding stuff into the system it causes all manner of problems between the ECU’s as they all “talk” to each other via the can bus. Even a badly soldered joint that’s causing resistance will cause mayhem.
Where I work now if theres a broken or damaged wire in any of the safety systems or in any other system that “may” impact said system then Mercedes insist on a new loom being fitted, absolutely zero repairs are allowed, period.
There is a very good reason for that.
I’m not saying all aftermarket stuff fitted is bad, but, the majority of drain problems I’ve seen over the years are a direct cause of it.