Classic Wiring a 13 Pin Trailer Socket - properly and as intended

[hef19898]

So, with the old harnesses as good as gone all the previously installed wiring went out as well. That includes the 13 pin trailer socket.

The car has what looks like a genuine indicator relay to be used for towing and the rear harness has a purple (weird color choice, the same as the interior lights, but it is the original color) behind the left rear lights. The installed socket has to go, the alumium housing is corroded enough to turn to dust.

Thing is, the car is registered as a towing vehicle. That has all kinds of benefits when it comes to MOT / TÜV and historical cars since the optical standards for commercially used vehicles are a lot lower than for normal ones. Which means I need to be able to tow a trailer, which requires a socket.

How do I wire said socket? I assume the lights go to the bullet connectors of the corresponding lights behind the left rear lights. The two earths can go directly to the chassis. I have no idea what the purple wire and the relay are there for then. I can always leave the fridge pin of the 13 pin socket blank.

Any ideas? Or, even better, any idea where I can buy a correct 13 pin socket and wiring kit for a 1982 RRC?

 

[miktdish]

There are loads of examples on Google.
13 pin sockets weren't around before 2008 ...

 

[Mark Piercy]

Do you need a 13 pin or can you use a 7pin socket?
Also where abouts in the world are you?

 

[hef19898]

Germany, and since she rated to tow 6.5 metric tons I thibk I need a 13 pin, at least properly installed. Already asked a while ago, and the pneumatic trailer break system required for the 6.5 ton trailers is not needed to maintain the towing vehicle classification.

Might be nice so for stuff like inflating tires and such, but absolutely not necessary.

 

[hef19898]

There are loads of examples on Google.
13 pin sockets weren't around before 2008 ...

That's what I found, so my first idea was to simply plug the lights into the rear harness as required, put two earth to the chassis and call it a day.

I have no idea if that is the proper way to do it so, because I assume the trailer relay is there for a reason...

 

[landowner]

Just put seven pin socket on and use a 13 to 7 pin adaptor when towing 13 pin

 

[Blob]

Just put seven pin socket on and use a 13 to 7 pin adaptor when towing 13 pin

I have a feeling that might not be an option, Germany has some funny rules about towing and the TUV might insist on it being 13 pin native especially if they need reverse lights on the socket. No idea whether TUV would test the live outputs or not but they'll certainly test the lighting functions.

Can't quite decide if the OP is saying 13 pin is or isn't necessary. I prefer 13 pin and fit that to everything as it's much neater, I have a 13>7 adapter of course because hardly any trailers have 13 pin anyway.

My guess would be that the relay is for a trailer tell-tale in some way, It will either need a buzzer or a light on the dash for the indicators won't it? Other than that, it's a case of tracing the wiring back.

Do you need the tell-tale light or buzzer for TUV? If so, a universal trailer relay will do the job for the inspection as they have the buzzer built in and are less than £30. This one even has the fog light cut out: Bypass Relay

 

[Blob]

No idea why that link won't link. Here's the long version: https://www.ebay.co.uk/itm/20243992...Te0AeimuDv4VhebITRPKcDp7c=|tkp:Bk9SR67AtsmFZg

 

[Blob]

Still can't get the link to work. Search for this on eBay: Universal 7 Way Bypass Relay PCT ZR2500 Towing Interface Inc Fog Cut Out
Item number 202439920209

 

[hef19898]

So far, they never tested the function of the socket, not even lighting. As I replace the complete wiring of the car at the moment, I thought of doing the socket as well. After all, the tow bar is the perfect recovery point!

Naively, I thought of simply plugging the indicator lights and so on to the respective car wires behind the tail light. If that's the "right", read professional, thing to do it seems to be easy enough.

 

[hef19898]

So, I learned something:

1) I need a 13 pin socket, those are mandatory by now for new trailers

2) if there is no dedicated kit for a certain car to connect the socket, apparently the connection goes directly to the tail lights

3) the constant plus and the ignition plus for the fridge present on the 13 pin socket will connect directly to the split battery in my case, no need to risk the main battery

That means some cables to go behind the left tail light and go to the respective cables, two wires from the split battery to the plus pins (pins 9 and 10), making the fridge pin also a constant plus (ok with me). Basically, just a bunch of cables and a new socket. Easy enough!

Still not sure how to connect the trailer relay, and what it is good for. Or required.

I am a noob when it comes to trailers and electrical wiring. Worse when it is both!

 

[Blob]

I think this is how it was done on the older stuff. It's unlikely that you'll be pulling too much amperage by adding trailer lights. The bypass relay is mainly used on newer vehicles that will throw bulb failure warnings if the resistance is wrong. The relay takes a micro pulse from the car and converts it for output on the trailer which is why it has a +12v input.

Just check to see if you need a warning light or buzzer for TUV on your classic. Here we have to have one or the other, effectively this means that you know your trailer indicators are working as it will beep or light something on the dashboard. I prefer the light because it's quiet. That's really the only reason I can see that you'd need to fit the bypass relay to your car.

 

[hef19898]

Good point about the Trailer indicator light, I do get an indicator light in the original dashboard between the fuel gauge and speedo... I'll ask! Sounds like a minor thing to add so.

 

[miktdish]

No idea why that link won't link. Here's the long version: https://www.ebay.co.uk/itm/20243992020??_skw=7+way+universal+bypass+relay&epid=20033702739&itmmeta=01K0P9DM07CD6V9DZFTQ4B63NM&hash=item2f225c0a51:g:JlIAAOSwu6VfhbdH&itmprp=enc:AQAKAAABAFkggFvd1GGDu0w3yXCmi1eEid5o2dExSxoFA6YMInCDyDlUon0XjAmFpoyDntbaplcx6KnihoqWvj/mER18NdY79Hst/71Se5+brsAjwVkfnoK4g9OY/lN1Yx/1BPqXuxGyyFHs26VX+LOb4BpaBSJeAEj9lKlxBWs8lHG9rs2UaDSSEBFY5hfNLb7L9b0KsVZ8F1ArXz3HbfDEF6GLA3DD0z0LF/iRNPcDrs9YfAhBxfpapjk3m3/p****RAtnO7ohpBA8iNN8OBKOyIiP8W9I26gAn1BS03KXIORQf1rgg8EYjc6G4yLW0vlqC5Te0AeimuDv4VhebITRPKcDp7c=|tkp:Bk9SR67AtsmFZg

Here is the link ....

Pardon our interruption...

and again without the XenForo error ...

https://www.ebay.co.uk/itm/202439920209

You don't need anything past the question mark as this is tracking info and other cookie detail that says where you have been, what you looked at, what type of computer you are using etc etc ...

 

[Datatek]

Just put seven pin socket on and use a 13 to 7 pin adaptor when towing 13 pin

Better IMO to fit a 13 pin socket and use a 13 to 7 adaptor as then you have all the connections for reversing lights etc at the connector.

 

[Datatek]

I have a feeling that might not be an option, Germany has some funny rules about towing and the TUV might insist on it being 13 pin native especially if they need reverse lights on the socket. No idea whether TUV would test the live outputs or not but they'll certainly test the lighting functions.

Can't quite decide if the OP is saying 13 pin is or isn't necessary. I prefer 13 pin and fit that to everything as it's much neater, I have a 13>7 adapter of course because hardly any trailers have 13 pin anyway.

My guess would be that the relay is for a trailer tell-tale in some way, It will either need a buzzer or a light on the dash for the indicators won't it? Other than that, it's a case of tracing the wiring back.

Do you need the tell-tale light or buzzer for TUV? If so, a universal trailer relay will do the job for the inspection as they have the buzzer built in and are less than £30. This one even has the fog light cut out: Bypass Relay

EU and I assume Germany require a dash bulb fail indicator or a buzzer for the indicators when the trailer is attached, the relay will be for that.

 

[Datatek]

So, I learned something:

1) I need a 13 pin socket, those are mandatory by now for new trailers

2) if there is no dedicated kit for a certain car to connect the socket, apparently the connection goes directly to the tail lights

3) the constant plus and the ignition plus for the fridge present on the 13 pin socket will connect directly to the split battery in my case, no need to risk the main battery

That means some cables to go behind the left tail light and go to the respective cables, two wires from the split battery to the plus pins (pins 9 and 10), making the fridge pin also a constant plus (ok with me). Basically, just a bunch of cables and a new socket. Easy enough!

Still not sure how to connect the trailer relay, and what it is good for. Or required.

I am a noob when it comes to trailers and electrical wiring. Worse when it is both!

On the ones I have fitted, the relay is driven using current sensing on the lines to the trailer indicators, bulb fail = no current so no dash indicator. The relay output goes to the dash. There were a number of different wiring methods depending on how long ago the device was made but 7 connections in some cases, 12V, Earth,LH indicator in & out RH indicator in & out and feed to the dash.

 

[hef19898]

Behind the dash, all the wires should have been original, I didn't check when I dismantled which wire went were, but especially behind the speedo assembly there are not that many options.

We'll see when I'm done, jist need to put already two properly colored cables from the split battery to left tail light for the constant plus and fridge pins of the 12 pin socket, much easier now with everything out.

 

[kermit_rr]

the RRC can't tow 6.5t? assume this is the gross train weight or maximum authorised mass?
there was no 13 pin socket until it was developed in 1987, so no wiring kit available at that time, nothing 'plug and play' into the existing loom

 

[hef19898]

the RRC can't tow 6.5t? assume this is the gross train weight or maximum authorised mass?
there was no 13 pin socket until it was developed in 1987, so no wiring kit available at that time, nothing 'plug and play' into the existing loom

Well, it can if someone made all the necessary mods, the pneumatic break and compressor have been removed by now, and got it registered as such. Lucky me one of the previous owners did!

The trailer indicator light is behind the printed circuit in the dash, so I assume that is going to work as is. It did previously, so there is hope!

By now I figured out a bunch more: Where the wires for diff lock light and reverse lights go from the engine bay! Means I have basically all routong points figured out, in theory at least.