OEM Subaru trailer wiring

Gidday Folks

I cannot believe this, but here it is ...

Roo2 has a "genuine" Subaru towbar. It has "SUBARU" and the compliance information stamped on it. It was fitted prior to delivery.

This afternoon, I spent over 2 hours investigating the non-standard wiring in my attempts to install the reversing light circuit ... This is covered by regulations that prescribe the wiring for small trailers.

The 7 pin connector plug on the rear of the car looks completely Kosher when opened. It just doesn't give the correct voltages at the various pins.

I then started to investigate the internal wiring of the car.

For starters: there is actually a large rubber grommet/plug behind the D/S rear light that is about 18" higher than the one that has been used for the trailer plug wiring at the bottom of the spare wheel well. This has to be the height of stupidity when there is a grommet provided, seemingly for this very purpose!

I pulled the actual trailer wiring socket apart, and it had the appropriate 7 colour coded wires running in to it, albeit some were loose.

Feeling the insulation taped connections, I could tell that there were joins in the wiring loom on the trailer connector side.

As I stripped off the layers of insulation tape surrounding the internal trailer wiring plug that is part of the car's wiring loom, I found more and more oddities.

Firstly, two of the seven wires had been taped back. This is a tad odd, I thought. I have 7 wires at the socket ... WTH is going on here?

Then I found that there were two whites and two browns on the socket side of the plug into the car loom. This is really bloody odd ...

[EDIT]

These two white wires and the two brown wires were connected to each other inside the trailer connector wiring loom, which has a Subaru part number on it ...
[end edit]

Out with my dissecting scissors, and started carefully cutting off the multiple layers of insulation tape. All of this looked perfectly original.

Out with the multimeter. That's odd. One wire that is available (but not connected to the trailer socket) has a constant 12V across it even with the ignition completely switched off.

[EDIT]

Photos of the car wiring loom and connector:




Close-up of the car loom female connection plug:




This is the tail plug of the wiring to the trailer socket. Note the two wires that were taped back - BLACK is for reversing lights; BLUE is for electric brakes. Both these are present at the trailer connection socket on the rear of the car ...


[end edit]

{Re-edited to reinsert photos deleted by forum software upgrades.}

to be continued ...

What really, really gives me the screaming irrits, is the lengths to which the people who fitted this (it was a pre-delivery fitment) went to disguise the fact that while the car end of the electrical connector looked fine, with all connections present, neither the electric brake nor the reversing light wires that are apparently present at the trailer connection were actually connected, but a 'head count' of the wires at each end showed 7 going in from the car's loom, and seven coming out at the trailer connection.

The joining of two pairs of two wires under the multiple layers of insulation tape at the point of attachment to the car's wiring loom, can only be construed as a deliberate attempt to mislead, requiring a return to the stealership to be "rectified", or a lot of time for some auto sparky, both of whom would charge for the exercise.

Provision for reversing lights has been a requirement for all trailers (and presumably car connections to trailers ... ) for all 7 pin connections (and above) since about 1989. Failure to properly wire the car for at least the reversing lights is inexcusable, IMNSHO ... .

also reserved

I've it all the factory trailer wiring plug pinout written down somewhere, i'll take a look for ya.

Thanks, Id. Much appreciated.

I`m usually stuffed with wiring.
Just can`t see where the electrons are going.....

Ratbag said:

Gidday Folks

I cannot believe this, but here it is ...

This afternoon, I spent over 2 hours investigating the non-standard wiring in my attempts to install the reversing light circuit ... This is covered by regulations that prescribe the wiring for small trailers.

Click to expand...

The simple fact is that - on the SG at least - the reversing light feed is NOT presented at the 6-pin trailer connector (R79) on the vehicle harness. This caught me out for a while.

Ratbag said:

Out with the multimeter. That's odd. One wire that is available (but not connected to the trailer socket) has a constant 12V across it even with the ignition completely switched off.

Click to expand...

The pinout of R79 -as I recorded it, and using Subaru's colour abbreviations - is as follows:

Pin 6 - B - Earth
Pin 5 - RY - Clearance/tail lamps
Pin 4 - BG - Left Turn
Pin 3 - WB - Stop
Pin 2 - LgB - Right Turn
and saved till last ...
Pin 1 - LR - +12V always (ex FB2 under dash).

So you will need to break out the reversing light feed from the D/S light harness (shown as BrY in the S/M) and connect that to the trailer harness. As to what goes on between the 7-pin PLUG and the 6-pin connector mating with R79, you're on your own.

Hope this helps.

Thanks Zippo.

The loom connector in my SG is 12 pin, IIRC.

I will finish my rant today, but what really p!sses me off is the deception, and failure to comply with a 30 year old standard!

From my Batphone

Ratbag said:

The loom connector in my SG is 12 pin, IIRC.

Click to expand...

???? there is a dedicated trailer connector (6-pin) provided by Subaru for trailer connector. There is also an in-line flat harness connector inside a nylonish sheath and anchored to the top of the floor pan adjacent to the spare wheel well. I hope that the original installation didn't cut into that ...

Don't have the time now to upload a pic, can do later if it helps. I know my Hayman-Reese towbar came with a generic tail attached to the 7-pin plug with a 6-pin on the other end, and a separate vehicle-specific harness (6-pin to 6-pin) that connected to the Subaru outlet. All plug and play, except for that reversing light feed - which I haven't needed yet, although I did break it out of the through-line to the light assembly.

Just had another look at the pics I took wayback when, and that main loom thing encased in the nylon protector doesn't actually look like a connector. Hmmmm.

Thanks Zippo.

Ratbag said:

The loom connector in my SG is 12 pin, IIRC.

Click to expand...

Actually 10 pin, per photos now attached to my OP.

zippo said:

???? there is a dedicated trailer connector (6-pin) provided by Subaru for trailer connector. There is also an in-line flat harness connector inside a nylonish sheath and anchored to the top of the floor pan adjacent to the spare wheel well. I hope that the original installation didn't cut into that ...

Click to expand...

It appears to connect to that.

All plug and play, except for that reversing light feed - which I haven't needed yet, although I did break it out of the through-line to the light assembly.

Click to expand...

That's what I am going to do when the "Occasional scattered showers, with a chance of a thunderstorm" we had last night have gone away. It delivered approx. 1" of rain, torrential at times, and thunderstorms for most of the night. Victorian weather forecasts are 'euphemistic', shall we say ...

Rather than my old time, crude method of slicing the insulation and soldering a tail to the (intact) wire, I will go down to SCA and buy a proper connector.

zippo said:

Just had another look at the pics I took wayback when, and that main loom thing encased in the nylon protector doesn't actually look like a connector. Hmmmm.

Click to expand...

I have this strong feeling that the existing tail from the trailer connection socket is wired in under this. I am not going to pull this to bits. Just add the reversing light feed and a fused 12V feed.

Judging from the gauge of the 12V wire off the loom, I reckon I should fuse it at around 5 amps.
What do you think about that?
Can the car loom wiring carry that much amperage safely from this gauge wire. It looks awfully fine to me ...

My reversing lights and tail/stop/indicators are all LEDs now, so the current draw should be minimal compared with the old festoon bulbs.

If I can buy another intact body plug for the bottom of the spare wheel well, I will pull the trailer cable tail out of there and feed it through the body plug behind the D/S tail light assembly. Neater, and 18" higher ...

This gets confusing, if not weird. I can envisage FHI changing the harness detail between early SG and late SG, yes a possibility, but not mid-split. Yours is an 06/MY06 and mine is an 07/MY07 yet your pic clearly shows a 10-pin connector (not fully populated) while mine has a 6-pin fully populated. The H-R adaptor for MY06-MY08 fits mine like a finger in a bum, so would be all at sea on yours.
Pic of my area as mentioned earlier: https://www.offroadsubarus.com/album.php?albumid=181&pictureid=1204

The wiring size in most "modern" cars is as light as they can get away with, but as long as the reversing lights are LED you would be good to go. Although I never got to install it before our trip, I have a 10W LED floodlight which is less than 1A, and even if your reversers were left on it wouldn't threaten the wiring. Now a 100W equivalent incandescent would be a whole different story in that situation, but in normal backing the short time wouldn't really be an issue.

Gidday again Zippo

It is indeed weird, mate.

Maybe the weirdness can be explained by the fact that the compliance info on my bar has "S U B A R U" stamped into the heavy steel bits. Perhaps this could even be a genuine OEM tow bar? The wiring loom socket and trailer tail plug are basically clones of the other OEM plugs/sockets in that area.

I know that most tow bars for Subies in Oz are most likely made by H-R with a "Subaru" compliance plate riveted onto them.

I also know that my car was originally purchased to order, and that the buyers waited 2-3 months for delivery. I have the original purchase papers, as we also have for RonnyRoo (it was the same sort of schedule - I must check out its tow bar, etc). It was delivered with literally a couple of kilometres on the clock, with the tow bar fitted when delivered; i.e. the car hadn't been driven around to the H-R agent in Toowoomba, then back for delivery (and the Milford cargo barrier in the case of RR).

BTW, thanks for the opinion on the wiring. I didn't think it would be much of a problem for laods up to around 3-5 amps.

Been to SCA and managed to buy a packet of break-out wiring connectors, even though they were absolutely certain that they didn't stock them ... :iconwink: :lol:.

They actually stock two different kinds ... Hopefully, this is one of them ... No guarantees today ...





Please excuse the really crappy photos. I'm not travelling at all well today. I forgot to get the tent to lid sealing tape at Bunnings - the main reason I went there at all ... .

In the second of the photos, one can see a metal bit that is like a bad copy of a Krone Connector. This is squeezed down over both the donor cable and the new tail cable. That's assuming that I know more about the SCA stock than they do - a potentially dangerous assumption today ...

{Edited 06nov24 to reinstate photos}

Ratbag said:

Been to SCA and managed to buy a packet of break-out wiring connectors, even though they were absolutely certain that they didn't stock them

In the second of the photos, one can see a metal bit that is like a bad copy of a Krone Connector. This is squeezed down over both the donor cable and the new tail cable.

Click to expand...

Yep, that's how those tap-in types work. Those things have two downsides - they open the conductors to atmosphere/corrosion, and they invariably sever a conductor or two in the cable. The Krone punch-down blocks are designed to receive single-strand cable ....

I would personally prefer the solder approach, but I have been described as anal more than once. Just to give you an idea how that works, when I installed the electrics for my H-R towbar I de-pinned the connector on the 6-pin end of the 7-pin-socket-to-6-pin assembly. Behind the D/S tail-light -or was it behind the return on the bumper? I don't recall - there is a slot with a grommet, through which the bare pin end was passed and re-fitted to the connector body. The grommet supplied on that cable assembly fitted that slot quite nicely, so as you said "up high", and some silicon ensured the seal was effective.

zippo said:

Yep, that's how those tap-in types work. Those things have two downsides - they open the conductors to atmosphere/corrosion, and they invariably sever a conductor or two in the cable. The Krone punch-down blocks are designed to receive single-strand cable ....

Click to expand...

Yeah, I use Krone connectors for network cabling and telephony (Oops! Did I just write that ... :iconwink: :lol. I actually have the Krone Master Installer's Manuals, volume 1 & 2. What's remarkable is that multi-strand Cat.5 will actually work properly for a fixed connector, and ditto using single core for patch cords. I have done both in emergent situations (replaced later, of course).

I would personally prefer the solder approach, but I have been described as anal more than once. Just to give you an idea how that works, when I installed the electrics for my H-R towbar I de-pinned the connector on the 6-pin end of the 7-pin-socket-to-6-pin assembly. Behind the D/S tail-light -or was it behind the return on the bumper? I don't recall - there is a slot with a grommet, through which the bare pin end was passed and re-fitted to the connector body. The grommet supplied on that cable assembly fitted that slot quite nicely, so as you said "up high", and some silicon ensured the seal was effective.

Click to expand...

So am I ... However, that part of my car is as dry as the inside of a dead dingo's xxxx, so I don't expect there to be any problems. I will also wrap the join up like an Egyptian Mummy - after testing continuity all round, of course.

If I can score a new grommet for the spare wheel well, I will re-route the trailer socket cable via that oblong grommet behind the D/S tail light assembly. Much more better ... :biggrin:.

^ All of the above ... This idiot (me ... ) just realised that he is buggering about with the air bag SRS system wiring and sensors at the rear of the vehicle! .

Fortunately, I realised this in time, before disconnecting anything!

I now realise that it is better to break into the wiring going to the P/S tail light assembly, as there is no confusion as to which set of circuits are for what purpose/s.

The break-out of the car's wiring loom to the P/S lights is one circuit, with one set of readily accessible and identifiable wires in it.

There are three circuits on the D/S of the car, only one of which has anything to do with the tail light assembly.

AFAICT, the car loom circuit wire for the reversing light at this point is BROWN with a YELLOW stripe on the P/S tail light part of the wiring loom (It changes to red with a blue stripe at the connector on the inside of the tail light assembly).
I need to confirm this. [EDIT] - CONFIRMED [end edit]

After peeling off some more redundant insulation tape off the trailer socket loom extension, I have discovered that the part is identified as being for "Liberty/Impreza 02/03".

Photos:

Part:



Break-out connector and wire colour coding. I have used a piece of black for the tail to the trailer loom, as this is the correct colour coding for reversing lights at the trailer electrical connection socket.





I have checked that I have 12V at the end of the tail, and that the P/S and D/S reversing lights still work ... :iconwink: . All .

Now all I have to do is solder the new tail from the break-out connector to the black wire going to the tow bar socket, then re-apply heat-shrink and insulation tape as required.

Ratbag said:

AFAICT, the car loom circuit wire for the reversing light at this point is BROWN with a YELLOW stripe on the P/S tail light part of the wiring loom. I need to confirm this. [EDIT] - CONFIRMED [end edit]

Click to expand...

Good to know that the S/M shows the right colour. As I was only needing stop/tail/earth for my wheel carrier attachment, the reverse wire ex the trailer PLUG (it ain't a socket...) is just taped near the 6-pin connector. The plan was to go after that Brown/yellow as/when/if I feel the need to enable reverse lights at the back for towing anything with rev-lights.

^ A bit like M/F in pipe fittings, it's sometimes tricky to know which is which ... Specially when they are sort of 'reversed', like the 240V plugs on caravans and such like. They are actually a plug, but look like a socket ... :lol:.

Any way, glad that my trials and tribulations with this have been of some benefit to someone else.

As can be seen in the final photos above, I have broken into the P/S car tail light loom, but on the D/S, where it leaves the main rear loom.

On another note, I had a closer look at the tow bar compliance plate. It is marked "SUBARU" and has a maximum towing capacity of 1,800 Kgs, with a maximum ball weight of 180 kgs. Talk about over-engineered! The car has a maximum towing weight of 1,400 Kgs (braked) and a maximum ball weight of 75 Kgs (N/A).

Looking at how the tow bar assembly is wrapped around all the structural bits of the back of the car, it appears that one would rip the back of the car off before damaging the tow bar. Comforting to know.

I now have the car reassembled. Still have both reversing lights on the car working (I took both of them off and cleaned behind them); and now have a functional reversing light pin on the car part of the trailer electrical connector.

I will run a separate lead for the 12V into the trailer tub and tool box later.

This arvo, I will start drilling the holes and running the wires for the trailer's reversing lights.

Tomorrow the tent goes back on the trailer - weather permitting. I have three friends lined up to help me with this. It will have to be dropped straight down on the sealing tape, so needs to be carefully aligned first. Otherwise it will damage the sealing tape. Since it weighs about 100 Kgs, and is about 2.2 x 1.5 m, it needs more than two people to manoeuvre it into place.