MK7 transit wiring help

[Osu817]

For my sins, I picked up an ex AA transit MK 7. I want the trailer electrics to work, but at the moment, I am having some trouble isolating the problem. it is a 13pin connector, which I am running with a 7 pin adapter.

Currently, everything except the indicators work on the trailer board.

I had a really corroded trailer light control unit, in the front footwell, which I replaced.

The wiring in the rear pillars is incomprehensible, due to removed light bars, beacons etc, which was done before me, by someone with a similar level of electrical knowledge as me, it would appear, otherwise I would have just swapped in a cheap 7 pin connector from the light cluster.

So - currently, without a trailerboard attached, all lights work fine on the van. With trailerboard, red lights work fine on both van and trailer, indicators don't work on either van or trailerboard. However, van seems to think they are, as it clicks at a normal speed, not the silly fast clicks when you have a bulb out.

I have a multimeter, and the indicator electrics in the socket give a reading of about 5v when I measure it with the indicators on.

Somebody please tell me the really obvious thing I am missing!

 

[johnik]

first thing i would do is ditch the 13 pin jobbie and stick a 7 pin socket on

 

[Barking Mat]

You get connectors which turn 13 pin into the old 7 pin.

 

[Osu817]

You get connectors which turn 13 pin into the old 7 pin.

I have one of those, reasonably sure that isn't the problem, but somewhere along the line, something makes my van indicators turn off when I plug in the trailerboard, and nothing happens to the trailerboard. I have tried three different trailerboards, to rule that out too!

 

[Ruffian]

Pull out the trailer control unit.

Fit fresh 7 core cable from bypass unit and 7 pin plug.

Sometimes waste more time and effort trying to salvage what's there than starting again from scratch.

 

[Ruffian]

Pull out the trailer control unit.

Fit fresh 7 core cable from bypass unit and 7 pin plug.

Sometimes waste more time and effort trying to salvage what's there than starting again from scratch.

Or try led bulbs in the indicator trailer board as may be overloading the system if detecting to many amps drawn

 

[m_c]

Genuine factory fit Ford trailer control module, or an aftermarket one?

Early revisions of the Ford ones used to fail reasonably often, with lights just not working (it works via a CAN/LIN signal, so doesn't connect in to the rear lights).

Aftermarket ones were even less reliable. If it's aftermarket, it would have piggy back looms on the rear lights. It could be somebody has bodged the piggy back looms in order to get the van indicators to work, as the way the aftermarket modules work, is to divert the indicator feed through the module before it goes to the van or trailer.

 

[Osu817]

Thanks for the replies everyone. I cracked in the end, after a day of learning to use a multimeter, I found an auto electrician who is going to take a look at it.

The issue for me is that it has two of most things in there, as I assume they were for the light board on the roof, and the trailer electrics.

I have isolated the fault to somewhere between the rear indicator and the trailer board, and the auto electrician said that what tends to happen is that the body control module shuts the power off if it detects a fault.

Pictures give you an idea of why I am struggling!

 

[knighty]

I've always pulled those modules out and dumped them, wired trailer plug straight into the back light loom right behind the lights

use a trailer board with LED bulbs so it doesn't pull much power

also... I've always put the trailer plugs inside the van on the pillar behind the light cluster (and up a bit higher) - that's the only thing that stops them getting smashed or full of water for us!

 

[m_c]

I was thinking of the newer Transit.

Older ones only used piggy back looms. Looks like somebody has bridged the piggy back looms, which means the trailer module probably isn't getting the required feeds.
The control module only handles the indicators, and the fog light cut out.

The other wiring/connectors would have been for the roof light bar, so you could just trace that wiring back to where it's been tapped into the van wiring, and cut it off.

 

[Moose McAlpine]

Having had 3 AA vans i can tell you that the company that outfit them do some absolutely shocking work some times. Not at all surprised.

 

[James1979]

I agree re AA vans. I had one and it was the same. Currently have one in my yard for a guy which is ‘ongoing’. It has all sorts of gremlins.

I’m having issues with my L200 in the same vein as OP. It’s ex utility and some cretin has cut out the water board Kit but not given any thought to terminating it properly. Confuses the hell out of the CAN system. It’s lights that are doing it, but I think it’s linked to the TCM, same as yours. I will post what I find when I get round to sorting it, in case it helps.

 

[AVI_8]

I would remove all of the non standard wiring to prevent future problems and it’ll make future fault diagnosis much easier as well. That’s a bit of a rats nest.

 

[Osu817]

Mine was solved today by a garage, who found that there wasn't a second power feed to the indicators in the trailer control module. Added fused power from the fusebox, and it all works now.

I would love to remove everything, but it really isn't worth it for the time taken, and the risk of me catastrophically ruining something! Especially as I don't know what is standard, and what isn't... Now I have found a really helpful auto electrician, I will just get them to deal with the rats nest - they can chop out if they need to if there is another problem.