Loss of power at permanent live and ignition live pins
 

My V50 has a 13 pin Volvo cable harness complete with trailer module and software update. My trailer has just a seven pin 12N plug so I've been using an adapter and all has worked fine. But I had also checked that pin 9 (permanent live) and pin 10 (ignition switched live) worked as I planned to use them in due course.

I have now started on converting the trailer to 13 pin and made up a new cable with a Menber 13 pin plug and proper 8x1.5mm2 and 5x2.5mm2 cable. Before wiring it into the junction box on the trailer I connected it to the socket on the car just to make sure everything worked and ... no power to either pin 9 or pin 10. As I had removed the old 7 pin plug and wiring, I checked the light circuits using a multi meter and all seem to be fine, apart from pins 9 and 10. I checked the continuity of the grey and orange wires (pins 10 and 9 respectively) from the pin to the end of the cable and they are fine. I likewise double checked that I had them in the correct position, which I have. I also checked the socket and it isn't live on pins 9 and 10.

I checked the 40amp fuse and it seems to be fine.

So where have I lost the power and how to fix it?

Check if brake lights and tail lights work properly, and turn off when they should

If you transposed the pin numbers, you would be transposing tail light with permanent power, and brake with switched ignition

Check also you have a proper ground on pins 3, 11 and 13.

Otherwise, check the fuses in the REM. the ignition feed and permanent feed are fused.

Many thanks for this speedy reply.

I'll check the pins again (I did check the three earths for continuity with the car frame) but I'm pretty certain I had got them right. Most diagrams you get, such as the one with the Menber plug, show the pins from the front, not the view when you're wiring them so I was very particular about having the correct view printed on a card in front of me while I did the connections. Plus, I also checked the numbers inscribed on the terminals.

The fuses you refer to sound like the likely culprits but what, and where, is the REM? And what might have caused them to blow since they haven't been used.

Have the pins 9 and 10 ever worked ? did you fit a NEW trailer module and have the software loaded ?

Pins 9 and 10 were checked and working when the towbar was fitted. It was a new Volvo cable harness and trailer module and the software update was done by my local Volvo dealer. I also had checked, in particular, pin 10 as I was expecting it to only go live once the engine was running but it was live as soon as the ignition was switched on. But that's another saga!

Pin 9 is fed directly from fuse 77 in the CEM under the glove box,

Pin 10 is fed directly from the trailer module which gets it's feed from Fuse 14 in the engine compartment fuse box ... The red wire going into the trailer module should be live all the time .

Fuse 14 seems to be ok. Getting at the trailer module to check the red wire is a pain! I’ll check fuse 77 in the morning but what would have made it blow?

Well, after grovelling in the passenger footwell to get at the fuse box located there it turns out that fuse 77 was blown. Now the question is, why? It’s only a 15 amp one so what does it supply?

OK, I replaced fuse 77 and that restored power to pin 9 (permanent live) but pin 10 is still dead. I double checked fuse 14 and it is fine.

What next?

It supplys Pin 9 and also the rear 12v Power outlet socket ( if you have one ) and 15 A is the correct fuse .

As I said above, with replacing fuse 77 I now have pin 9 (permanent live) working but still nothing at pin 10 even though fuse 14 is ok.

Where do I look next?

if you have 12v on the thick wire going into the trailer module and nothing coming out on pin 2 of plug A ( the one that goes to Pin 10 on the socket ) then either the Trailer module is faulty , or it has not had the software or it is not getting the network signals , if the rest of the lights work it is likely to be the trailer module ..
But make sure there is continuity between the pin 10 in the socket to the pin 2 in plug A on the trailer module First .

It’s quite a chore to get to the trailer module - half the interior trim needs to come out!

As I said above, the module had the proper software upgrade when the tow bar was installed last year. And I know I did have power to pin 10 afterwards as I specifically checked whether it came on with just the ignition or whether the engine had to be running. In the event, I discovered it came on with just the ignition so I’m now in the process of fitting a voltage sensitive relay on the trailer to trigger the auxiliary battery charging connection only once the engine is running. I was planning to connect the relay to pin 10 but if I can’t get it working I might just connect it to pin 9. That’s the usual one for battery charging anyway.

But I’ll maybe have a go at stripping out the trim tomorrow to get to the bottom of this. Very odd, and very frustrating.

Of course it’s not impossible that the wire for pin 10 has come loose in the socket and somehow shorted pin 9 and in doing so blew the fuse. It’s probably worth checking the socket before dismantling the interior trim!

OK, I got the trim panels off this evening and the heavy red wire with the grey connector is presumably the power feed to the trailer module (via the 40 amp fuse 14)? Since everything works apart from pin 10, it seems reasonable to assume that power is getting to the module so the question is why is it not getting to pin 10. I tried to extract the plug with all the wires to the tow bar socket but without success. It’s obviously latched in place but I couldn’t work out how to release it. I’ll have another look at it in the morning.

It’s strange that the fuse for pin 9 blew and perhaps that’s related to the loss of power to pin 10, but how? Does pin 10 have a separate fuse other than the general 40 amp one that presumably covers everything apart from in 9. And how does pin 9 connect to the 15 amp fuse since pin 9 is powered from the trailer module?

Edit: OK, looking again at the instructions for connecting the trailer module I see that there’s no orange wire (pin 9) connected to the trailer module plug so pin 9 must be fed from the circuit that supplies the 12v socket in the load compartment - hence the 15 amp fuse 77.

pin 9 is separate to pin 10 , pin 9 goes direct to the fuse 77 which comes from the battery .

No , pin 10 comes directly out of the trailer module , have you got live going in the red wire to the trailer module and coming out at pin 2 on plug A going to the socket ? you need the ignition on of course .

yes you are right about pin 9 being fed by the same wire as the 12v power socket .

I suspect the trailer module at the moment ..

I haven’t yet been able to extract the grey plug with the heavy red power cable feeding the trailer module so I can’t be sure that the module is getting power. I was getting voltage at the socket on the tail light pins but when I think of it, not the full 12+V. So perhaps there’s no power in?

I’m not sure what you mean by “plug A going to the socket”. Is that the 12 way connector that connects the tow bar socket wiring to the module?

yes that is the plug , all the wires should be white .... but have black numbers printed on the ends .

The wires to that connector are all coloured in line with the coding for the 13 pin socket and, according to the installation instructions, pin 2 is not used so there’s no wire there.

Is that a Volvo wiring loom?

Admittedly mine is 6 years old now but as clan says all conductors are white with black number identification.

The volvo socket is also potted in that you cannot get to the terminals the wires are connected to on the 13 pin socket you plug into on hitch up as the back of the socket is filled with a jointing resin that sets hard.to prevent water ingress.

Paul.

Yes, it’s a genuine Volvo cable harness for the 2005 V50.

Here’s the relevant page from the instructions.

It's a mystery , yours must be a very early car or prototype kit all the volvo wiring diagrams point to the 13 pin loom wires as being white ...

anyway do your tests and see what you come up with ...
you need a solid 12v capable of lighting a headlamp bulb feeding the trailer module .

Here’s the link to Volvo's accessories and the instructions for fitting the cable harness I bought which clearly show the individual wires are coloured as per the 13 pin socket colours - https://accessories.volvocars.com/In...utomatic/R.H.D

I’ll finish the rewiring of my trailer and then connect it to the car and see what happens. Presumably the red power feed is a constant 12 volts so that the trailer lights work even with the ignition off?

Yes constant feed to the trailer module
No , the trailer module supplies an output to the relevant trailer lights when it gets told to by the car's computer network system . The trailer module listens for commands from the car to switch the trailer lights on or off . It will probably not work if the Caravan has LED lamps ... This was allowed for from about 2012 ..

Thanks. Since the lights are presumably powered via the feed to the trailer module it needs to be constant 12v so that the trailer lights can work with the ignition off (which they do).

The instructions for the trailer module specifically state that it won’t work with LED lights on the trailer.

Related to this issue of pin 9 and pin 10, pin 9 (permanently live) is protected by the 15 amp fuse 77 but is pin 10 (ignition controlled live) protected only by the 40 amp fuse 14? I want to provide a charging supply to the trailer battery that only kicks in once the engine is running. The easiest way to do this seems to be to fit a voltage sensitive relay (VSR) on the trailer to pin 10 and use the output from this (with a 15 amp fuse) to charge the battery. Alternative I could use the output from the VSR to trigger an ordinary relay to connect the output from pin 9 to charge the battery. The latter setup replicates the 'habitation' relay in a caravan but seems unnecessary for the specific purpose I have in mind. Is there any reason not to use pin 10 to directly charge the battery in this way?

Yes pin 10 has the 40 amp fuse but i daresay there is electronic protection in the trailer module as it will be switched by a transistor device .

Well, whatever the problem was, it seems to have resolved itself! I connected up the trailer using my new 13 pin plug and cable and everything worked including pin 9 permanently live and pin 10 going live once the ignition is switched on. I’ve connected pin 10 on the trailer to a voltage sensing relay which works as expected, i.e. no voltage output until the engine is running and the alternator is putting out 14+ bolts. So that’s what I’ll use to charge the trailer battery.

I can only assume that without the trailer being attached the trailer module doesn’t send power to pin 10 although in the past I was able to measure 12 volts at pin 10 in the towbar socket. But whatever, it now works.