e70 Trailer Wiring - No Brake Lights on OEM Kit

[tawa 150]

Hi All,

I installed an OEM electrical kit to go with a locally made tow bar, but when trying to test it I've found I can only get it to function in US mode (LAENDERVARIANTE_AHM  -  COUNTRY VARIANT TRAILER MODULE set to US) and using the 4pin adapter, US combines the indicator with stop lamps so the indicators both light up when the brake light is pressed, and the other line covering running lamps (on when lights are on). Which is all well and good, apart from us not being in the US and having entirely different trailer wiring/laws over here.

So I changed it (back) to ECE, and now the indicators work without the brakes on that circuit; but I can't find where the brake lights are supposed to be run out to. The kit came with the Round 7Pin Blade connector which has the following wiring printed on the cap

Right and Left turn work as advertised, as does the +12V (and Ground), reverse doesn't light up (after getting a freind so it didn't go into park every time I got out to look), electric brakes don't light up, tail lights do come on/off with the car's park lamps.

The system integrates properly with car otherwise, showing the Towing Icon in place of the rear PDC radar area, and it does come up with rear brake light fault. Is it something as simple as not enough load on the Brake light circuit (I'm using some LED bulbs I had lying around) and it not sending power to it? Or is there some wiring changes I need to make to the AHM module harness to bring the right signals out to the connector? Or is it a bad module or something, I'm a bit lost which avenue to pursue next...

It's raining out so I pulled the wiring diagram from ISTA and it looks like a few wires might not be there, 10 listed as going to the Trailer Socket but only 7 in it, , anyone come across something like this before?

[aja540i 1906]

That is an American style trailer plug, it has combined turn /stop lights. Electric brake output is for trailers with electric brake controllers your module possibly doesn't have an output for that. The brake light fault is probably because of the LED indicators, you can get in line resistors to fix that. Is the module you got a US spec one?

[tawa 150]

Thanks Andrew, you're right in that the electric brakes line just ends up at a plug as I don't have an electric brake controller installed.

I got out there today to trace out wires, long story short is the harness is different between US and EU versions (probably could have seen that coming if I'd realised that trailer wiring convention was different between countries). Currently I've swapped the pins on the AHM connector from #14 Parking Light to #1 Brake light to get the brake lights out to the trailer, though there is no space left for a reverse light, which there wasn't an option to swap for anyway as the pin size was different. I don't think reversing lights are mandatory but will order some pins so I can re-terminate and move wires around to make it work with our 7pin plugs. I do like the US style plug though, the blade connections look far superior to the NZ split pin style which are forever needing a screwdriver stuck down them to get them to make a connection.

The wiring diagrams in ISTA were super helpful for this too, would recomend.

[tawa 150]

Well the trailer module didn't quite last 2 years. Hopefully it was just a dodgy specific module rather than a 2-year consumable! Just put another one in and it works, so will make use of the FCP Euro returns policy.

Will put the reverse light in while I'm doing things... And also drop the pinout here in case others are going through the same process.

[tawa 150]

Another update on this, since I did it, it has flickered with LED lights on the stop lights, and thrown bulb faults on the indicators. Since I had wired the US receptacle in parrallel with our 7pin flat style one, I made a dummy plug with resistors on indicators and stop lights. This solved the indicator showing as bulb faults, but still had flickering stop lights, read somewhere this could be due to the test pulses checking the top lights on the car's bulbs (the trailer module takes the brake signal in through a wire connected to the brake lights) and that taking it from the high stop light is a better option since there is a filter on it. Sure enough, moving that wire got rid of the flashing stop lights. So now it works all good!