Trailers and controllers and wirings and stuffs... (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Sundowner

Epic Mediocrity
SILVER Star
Joined
Oct 16, 2014
Threads
6
Messages
344
Location
Virgo Supercluster
Post-project info, tips and tricks: read this first!

This is a post-completion edit-in-progress; the original first post begins below...but this will be an easy way to make sense of all of the information that was discussed and the wrong turns that were taken, in the hopes that the next person who attempts a 12V trailer circuit will have an easier time than I did. This being said, we can proceed to A Few Short Words On:

The Overall Point

My purpose in constructing a 12V trailer-light setup was - obviously - to pull a 12V trailer behind a 24V Cruiser...but it was also to get a functional 12V system on board, and to keep that system as low-profile and reliable as is possible; to be honest, I didn't want any portion of it to be easily or readily visible, but I still wanted easy access to the components. Locating the bulk of the items within the left rear quarterpanel and accessing them via the removal of the interior trim panel accomplished this, albeit at a cost of some light fabrication and medium-strength profanity. Other locations are available.

Components

I elected to keep factory/OEM quality wherever possible; this presented several challenges. Relays, wire, connectors, modules... you name it: they were all somewhat difficult to find in the US on short notice. If you also eject to go for an OEM level of construction, you'll need to plan ahead and find a few things that confounded me for a bit:
  1. Factory taillight connectors. The correct unit is the Sumitomo MT-series .090 6-Position Special-A. I'm not making that name up, by the way: you'll need a half dozen of them, and you can find them here, at Eastern Beaver.
  2. If you follow my Diode Reversal Variant (to be noted below) you'll need to find a diode-flavored ISO mini relay - four of them, to be exact - and if those are all you can find, you'll have to follow the Reversal Variant. The Bosch 0332209204 are correct for this application.
  3. Factory-spec wiring for the taillight intermediate harness - i.e. the link you insert between the separated factory connectors in order to shunt various signals into your relay block - is available from LSWiring. You'll need 20AWG in whatever colors you find in your harness for the following circuits: both turn signals, the brake/stop, the running lights, and the ground/earth.
  4. A 4-position block for the ISO mini relays. Hella makes a nice one; other options are available. Word to the unwise: buy extra spades.
  5. The actual 12V converter and fuse block are somewhat immaterial, as long as they cover your needs...so before you get started, plan out as much of your 12V bus as is possible and size things accordingly. I bought a 30-amp Victron Orion unit - the 24/12-30, to be exact - and I paired that with a Blue Sea 5025 fuse block. Both will fit in the space allowed.
  6. I'm not going to place a link to any specific battery cable and/or primary wire, so just buy the best marine-grade, pre-tinned stuff that you can get. Check local marine suppliers, if you have any: often, you can get short pieces for 30% to 50% off.
Tools

The electrical tools are standard: multimeter, strippers, etc. You'll want an actual cable cutter if you don't have one - Klein does a good job with this one - and for all of the small terminals, you'll want to pick up some decent crimpers. Also, be wary of the primary 24V leads: depending on how you route/size them and where you place your converter, you could end up with 6AWG - if not larger - on either/both sides of that unit. For that size terminal a hydraulic crimper is almost necessary, and they aren't cheap; I had battery cables and winch cables to build as well, so I bought a hydraulic crimper from Temco, but you can hammer crimp them as well...or just have someone else make the cable. Either way, be forewarned.


To be continued...


I've been futzing with the search function and not coming up with any good answers, so that's my probably my fault and ineptitude...but nonetheless, I'm having a real time of it trying to get some basic answers on trailer wiring on my 73.

I'd like to get a 7-pin connector and a brake controller installed, but I'm not finding a lot of info on how anyone has done it. I know there's absolutely no such thing as a kit, so I know I'll have to figure something out for myself...but the main question is this: am I going to have to run a separate 12v drop to the brakes themselves and leave the wiring at the 24v of the indicators and stop lamps? If so - or if not so - what's the best method for the wiring pulls to do so? Direct from the battery (or a rear sub-panel) for the brakes, and some careful tie-ins to the indicators/stops? I know the electrics can be fussy on these, so I'm really not interested in hacking it all apart and screwing it up...so I'm inquiring before I start cutting wires.

Also, I saw a couple of posts here and there that said the braked towing capacity on the mid-wheelbase models was 3500kg, like the longer ones. Is this correct? It doesn't seem correct, to me.

Thanks in advance for any help.
 
Last edited:
I've been futzing with the search function and not coming up with any good answers, so that's my probably my fault and ineptitude...but nonetheless, I'm having a real time of it trying to get some basic answers on trailer wiring on my 73.

I'd like to get a 7-pin connector and a brake controller installed, but I'm not finding a lot of info on how anyone has done it. I know there's absolutely no such thing as a kit, so I know I'll have to figure something out for myself...but the main question is this: am I going to have to run a separate 12v drop to the brakes themselves and leave the wiring at the 24v of the indicators and stop lamps? If so - or if not so - what's the best method for the wiring pulls to do so? Direct from the battery (or a rear sub-panel) for the brakes, and some careful tie-ins to the indicators/stops? I know the electrics can be fussy on these, so I'm really not interested in hacking it all apart and screwing it up...so I'm inquiring before I start cutting wires.

Also, I saw a couple of posts here and there that said the braked towing capacity on the mid-wheelbase models was 3500kg, like the longer ones. Is this correct? It doesn't seem correct, to me.

Thanks in advance for any help.
See this thread in your search? Trailer Lights Logic Circuit & Step Down Voltage Converter - https://forum.ih8mud.com/threads/trailer-lights-logic-circuit-step-down-voltage-converter.43609/

Built the step down based on that logic for my rig a few years ago. Works a champ. Also run a 12V Redarc brake controller. Already had a house battery in the rear so pulled 12v from there for it.

Redarc does have a fancy "trailer light reducer" but I don't think it's available in the US and they are proud of it based on the cost.

30A 5 Circuit Compact Trailer Lighting Reducer - https://www.redarc.com.au/compact-trailer-lighting-reducer-30a-5
 
See this thread in your search?

Sure didn't, so thanks for posting it. I have very little luck with the search function on this platform; it's a perennial issue.

I'll give both of those links a very long look; from first glance it seems like the separate-signal issue is being handled pretty well. That's the part that's been confusing me the most. Thanks for both links. 👍
 
In addition to what @Guyute posted, here's some more research info for you:

Redarc makes a 24v trailer brake controller and probably has a ready made harnesses for 70 series if you check the Australian site

Some 70 series harness info here

where to locate plugs at the rear bumper for trailer light harness to attach to- at least on troopies, probably other 70 series too:

And some wiring/voltage drop relay intel here (probably modeled after the mud link in the @Guyute post:

There is a lot of info on trailer lights/brakes here on mud, just hard to locate in the various threads. Best to use google search engine with ih8mud at the end to find what you are looking for.

Search postings by @FJ73Texas and @Blomdala, they have both tackled this to some degree.
 
You guys are knocking it out of the park today...and yeah, I'd buy a ready-made harness in a heartbeat if someone actually has one available. More links to check... 👍
 
I have plenty of room to house a relay or converter - center console, rear toolbox alcove, whatevs - but no house battery space... so, that kind of solution will work for me. And a legit step-down needs to happen anyway; the PO had an aftermarket stereo installed and their solution for 12v was to tap one battery...

Guess what happened to that one battery? 🤬
 
What I did works for me but I don't really even tow. The main reason I did what I did was to have non-factory wires to tap and splice into for the kaymar bumper lights but you could do the same for trailer lights too. I didn't have to cut or splice a single factory wiring for the kaymar bumper lights using a plug and play kit with the right connectors.
 
So after doing some thinking and reading - thanks again for that - it seems like the logical first step is to get a solid 24v to 12v voltage converter installed. I looked over the options from Redarc and there are about a billion of them...but only four are on the US site. I know they're not the only game in town, as well...but I have some research to do, regardless.
 
So after doing some thinking and reading - thanks again for that - it seems like the logical first step is to get a solid 24v to 12v voltage converter installed. I looked over the options from Redarc and there are about a billion of them...but only four are on the US site. I know they're not the only game in town, as well...but I have some research to do, regardless.
Believe Victron makes decent ones and are readily available here.
 
Believe Victron makes decent ones and are readily available here.

Cool; thank you! I'll check them out as well.

Thankfully the relays are easy to find; a junkyard with some Japanese stuff should yield decent Denso units.

Edit: this is a stupid question, I'm sure, but because I'm voltage-stupid...how do I actually size and select a converter?
 
Last edited:
Cool; thank you! I'll check them out as well.

Thankfully the relays are easy to find; a junkyard with some Japanese stuff should yield decent Denso units.

Edit: this is a stupid question, I'm sure, but because I'm voltage-stupid...how do I actually size and select a converter?
Victron makes very good products. As far as what size converter, it depends on what loads (amps) you need it to power. If you are using it to power 12V electric brakes and lights look at what the max current required for the brake controller is and size it slightly larger than that. Victron makes a 70 amp one that would likely cover all of your 12 volt needs. They also make 8, 10, 20, and 40 amp voltage converters. If you only need to power 12V lights you could look at "buck converters", they can only handle a few (up to 10 usually) amps but are small and easy to wire in line.

You will need to be mindful of what your alternator is capable of putting out if you start adding lots of current needy appliances. And, make sure all of your wiring is sized and fused correctly.
 
In addition to what @Guyute posted, here's some more research info for you:

Redarc makes a 24v trailer brake controller and probably has a ready made harnesses for 70 series if you check the Australian site

Some 70 series harness info here

where to locate plugs at the rear bumper for trailer light harness to attach to- at least on troopies, probably other 70 series too:

And some wiring/voltage drop relay intel here (probably modeled after the mud link in the @Guyute post:

There is a lot of info on trailer lights/brakes here on mud, just hard to locate in the various threads. Best to use google search engine with ih8mud at the end to find what you are looking for.

Search postings by @FJ73Texas and @Blomdala, they have both tackled this to some degree.
Australia got 12 volt versions not the 24 volt cold weather specced ones
 
Okay, if I basically just have to count amps, it's pretty simple. The only 12v electrical add-ins that I have planned are a drop for my fridge and then whatever I have for the trailer. I have a set of fog lights to install at some point, but those are 24v.
 
Okay, if I basically just have to count amps, it's pretty simple. The only 12v electrical add-ins that I have planned are a drop for my fridge and then whatever I have for the trailer. I have a set of fog lights to install at some point, but those are 24v.

That's about it. If you have LED trailer lights they may be able to handle 24v, most, but not all LEDs have a wide range of acceptable voltage. Also, many fridge compressors run on 12/24v so you may not need a converter for that either.
 
Any euro specced 24v brake controllers?

There might be some fleet-rated stuff; 24v is pretty standard in that realm...but regardless, I also have a 12v system on my truck, so to my mind it makes more sense to 1) have a trailer that can be used on either vehicle, and 2) change the least amount of stuff possible to make #1 happen. So, I was thinking that if I could get a solid, clean and safe 12v from the Toyota's 24v system, I could accomplish all of my goals. I just don't know enough about The Voltages to make that happen without a lot of The Online Help. That's where you guys come in. ;)

That's about it. If you have LED trailer lights they may be able to handle 24v, most, but not all LEDs have a wide range of acceptable voltage. Also, many fridge compressors run on 12/24v so you may not need a converter for that either.

I need to check and see what mine will do...and it's actually where I can find it, after the move. Amazing piece of luck, that...

I started looking at converters, by the way. I like the Victron ones; they have a LOT of stuff available here (US). The Orion series seems pretty good, and as stated they have some 40- and 70-amp models. I think I could easily do the 40 and have plenty of capacity, and it will fit in any of the three or four places I've found for it. That little side-access compartment on the left side of the rear passenger area would be great...or the rear tool enclosure...or in the bottom of the center console...or basically anywhere that I can stick it and place it adjacent to a 12v bus block with space for some relays.
 
Last edited:
Quick verification question: since I'll be using the DC/DC converter as a 12v power supply, I need an insolated unit, correct? That would provide a completely clean 12v supply whereas the non-isolated, common-ground unit would...not? I've been reading on the subject, and it seems that most people are using these to charge a 12v separate/house battery, in which case they're using the isolated units; if I just replace the battery with my 12v bus block, then it seems like the isolated unit is still the correct application, yes?
 

Users who are viewing this thread

Back
Top Bottom