Summary

This thread is about the design and build of a Relay/Fuse box based around the Eaton Bussmann 31m-000 CAN bus controlled power distribution system.

Either you have plenty of power for all your stuff, or you don't, or you want a relay box "just because" (and there's nothing wrong with that). There are simpler, more cost effective approaches than this build. However, this thread may allow others to learn from my mistakes, and perhaps pick up an idea or two along the way.

Introduction

We were looking to add a Relay/Fuse box to our 2020 TRD ORP. There are a lot of good choices with plenty of documentation in these forums, and at other sites. However, as with our 4Runner, the approach we are taking leads us well off the beaten path.

The idea of using the Bussmann RTMR seemed like a fun DIY approach. The documentation provided by bodenzord/tacozord is fantastic. Unfortunately, there is change in the 2020's electrical layout that makes this more complex. Toyota put a secondary engine-compartment relay/fuse box in a position that can interfere with driver-side trays, and winds up being even more intrusive for systems (such as the RTMR) that have anything extending underneath the tray.

That lead me to find and consider the Bussmann Series 31000 Single Vehicle Electrical Center (VEC). Those units have similar capabilities to the RTMR, but don't require all of the DIY wiring of the box, and are all above the base-plane of the unit. Sane people, just looking for a simpler option than the RTMR might want to stop reading this thread and consider those.

While looking at that line of products I ran across the Series 31m mVEC. It can handle more circuits, and what was even more fascinating, it is CAN bus controlled. A CAN bus is the same approach used by many of the 4Runner's built in controls (along with a LIN bus), and is also the approach used by two other less DIY options: Switch Pro and SPOD.

The 31m module alone lists for ~$300, but can be found for as little as $235), and of course needs switches and connectors to be turned into a complete system. A full build-out would cost a bit more than a Switch Pro for a system that does have the advantage of additional fuses beyond those for just the relayed circuits, but would be physically much larger. Looking at a number of factors the Switch Pro 9100 seems to me the best choice of the three options (YMMV). Again, this is a chance to stay on the traveled path. You have been warned.

However... in my searching, I happened to find a couple of the Eaton/Bussmann 31m systems on eBay that had never been put into vehicular use. One of the listings also came with a CAN bus switch panel, a USB to CAN adapter, and various plugs and connectors. So cost of entry into trying this 31m approach for a one-off installation was reduced. Famous last words: "This trail doesn't look too bad at the turn-off."


Plan

I'm going to do this as an on-going build thread, rather than a post-completion tutorial. After all is done, I may be able to create a summary/instructions if someone else wants to go this route. Or..., I might have some parts to sell on eBay...


Status

• Ordered and received a 31m-000 with the HMIsystems switch panel (482CRM-8) and various connectors via eBay.
• Ordered all the other tools, connectors, wiring that should be needed (yeah, right), and some of this material has started to trickle in.
• Ordered a 110 -> 12V power supply to set up a bench test config
• Ordered a PowerTrays blank tray to use as a base platform, along with battery cables, master fuse, and circuit breaker
• Designed a 3D model of all the parts, including a secondary tray to help solve the access to the 2020 secondary fuse-box issue.

The secondary tray approach is worth particular mention. I'm going to cut a hole in the base tray so that the stock secondary fuse box can be reached. That should also make it easier to reach the bolt-holes on the fender side to attach the main tray. The secondary tray will be either directly on top of the main tray, or elevated slightly for clearance purposes. It will be attached with bolts on the perimeter, so it can be easily removed if access is needed to the stock relay box. The secondary tray also will allow me to place a circuit breaker in an upright location.


Next Steps

• Wait for the 12V power supply to arrive. That's the missing long-pole in the tent for the time being.
• Continue to try to reach out to HMI systems to see if my concept for shortening the switch set will work.
• Document the materials and sources I've found so far.

I've attached a couple of photos of the 31m unit, the switch panel and some shots of the 3D model (nice to know that everything seems to fit ,with the exception of one bolt-hole that might wind up being a bit wonky). With all this at-home time I started to learn Autodesk Fusion 360 - they have a free license for personal use.

Attached Images