Fuse block inner magic


Veteran Member
Jun 17, 2003
Salem, OR
2015 Brilliant Black Audi Q5 3.0TDI, 2014 Tempest Blue metallic Jetta Sportwagen TDI, 2002 Blue Eurovan Weekender BHW TDI
I'm working on a BHW TDI swap into my 2002 Eurovan and I'm trying to combine the fuse box from the Passat as much as I can with the van. I've found this website HERE which is fantastic for the individual wires coming to the back of the fuse box/block. I've also downloaded the appropriate wiring diagrams from Elsawin.

My question involves the inner workings of the fuse block, and I was hoping that I wouldn't have to pry mine apart to see the innards. I'm curious how the relay spots get their wiring, and if I'd be able to splice relays that are extra from the Passat into the T4 fuse block since there are open relay positions. Does anyone have a diagram for how the specific relay positions and fuses get their power? Am I making this too difficult on myself? I've got a few loose relays and fuses from the Passat harness that I'd like to combine/incorporate into the vans wiring so its cleaner and less odds/ends.

I've posted on the UK T4 van forums as well, but figured I might get more MK3 knowledge here.

I found a spare MK3 fuse block on ebay for a few bucks and it should be here later this week. I'm hoping to open it up and see how the internals are routed. Just wondering if anyone here has attempted to add relays and or fused relays to an MK3 fuse block?



Steve Addy

Top Post Dawg
Aug 7, 2002
97 Mk3
You're making this too difficult and it will undoubtedly become more problematic to try and do what you want to do. The open spaces on the fuse block for some models / equipment might be able to be used for other things but you're also talking about moving further away from the manufacturer's setup and that would make things much more difficult to diagnose if there was a problem....or for the next owner should you decide to sell.

I had no trouble combining my 1990 Passat wiring harness with both a Mk3 tdi (engine) and B4 (AC, cooling, radio etc) and making it work. I left it as native as possible so if problems did crop up I could reference wiring diagrams produced by VW in an effort to resolve the problem. For me it was just easier (even if not cleaner) to keep things the way VW did it, and if that meant vacancies in the fuse block..well, that happens.

And as for those vacancies, I have to believe that VW didn't use those relay positions because there was some kind of internal conflict in the box itself that rendered it unsuitable.

Sometimes the easiest solution is really the best.


Vince Waldon

Top Post Dawg
Apr 25, 2009
Edmonton AB Canada
2001 ALH Jetta, 2005 BEW Wagon
If yours is like most VW relay blocks I've pulled apart it's a fixed and intricate sandwiched grid of tin strips, die-cut in specific patterns to connect specific current paths as required.

So yup, not easily adaptable to anything other than exactly what it came out of the factory to do.