Electrical: Tailgate Wiring Solution - Once & For All?

[TheHungriestBadger]

Hi all,

So, bear with me here, it's gone 4am as I write this. Everyone is sick of the tailgate wiring issues, right? I was looking through the paperwork for my '90 245, and it's already been through three of them since 2000, and now it's looking for a fourth (not quite 100% rear wiper operation, no central locking on the tailgate... Probably borrowed time before the MOT-able things start to go as well).

How about I design essentially a 'megaRelay' that slips inside the tailgate (there's got to be room, surely? There's already a wiper motor in there after all), and all it requires is a single low-resistance switched positive, and maybe one or two other tiny wires for sending a data signal - I'm confident I could handle that wirelessly, but I don't necessarily trust the cyber-security of wireless over a wired equivalent.

This whole system would consist of two small circuit boards (which could probably be packaged down the line as relays with a ton o' pins if desired):

- One would probably end up under a kick-panel somewhere, near all the existing relays, and would have all the existing connections 'terminating into it'. This would turn the existing power connections into simple signals (i.e. the current-carrying rear demister would now be a binary on/off signal).
- The other would be in the tailgate and would route the proposed single switched live, as appropriate, to the relevant accessories. This would be achieved based on the aforementioned data wire(s).

Essentially, this would keep all the existing functionality, it would just condense the 8 or so wires that are currently mounted in the hinges, into only a couple of wires. Given these would have to be added in anyway, they could then be brought inside the car, and any section exposed to flexing be made pluggable at both ends allowing for massively increased serviceability if it were to go wrong.

I think I'll leave the conceptual rambling there for now, please let me know your thoughts and also please play Devil's Advocate for things I'm likely to overlook. Obviously, the first victim of such an experiment would be my own vehicle.

P.S: A rough block diagram is attached and linked, wiring colours should be fairly accurate, but this is only for demo purposes.

Link: https://drive.google.com/file/d/1XdQ...usp=share_link