Technical All rear lights failed Oct 2021 Ducato 140 2.3D (Swift motorhome).

[Tanconsult]

Sudden lighting failure after engine start; warning on dash of indicator lights both sides out. Cable to towbar fitting (bike rack) also has no lights. Indicators & headlights/sidelights at front, running lights down sides, mirror repeaters all working fine. Looks like an electronics failure somewhere in the front (don't believe all the bulbs have simultaneously blown!) but wondered if there is any route forward other than a garage visit.

 

[kik]

Check all ground wires starting with the negative terminal and tied to the body. I loosen them, lightly spray with contact spray and tighten them again.

 

[Tanconsult]

Sorry but I live in a far-off country (Scotland...) and your event is just too far away.

 

[Communicator]

Sudden lighting failure after engine start; warning on dash of indicator lights both sides out. Cable to towbar fitting (bike rack) also has no lights. Indicators & headlights/sidelights at front, running lights down sides, mirror repeaters all working fine. Looks like an electronics failure somewhere in the front (don't believe all the bulbs have simultaneously blown!) but wondered if there is any route forward other than a garage visit.

As your vehicle is a motohome, the lights at the rear will have been installed by the converter (Swift). Also the rear of a motorhome is generally made of non conducting materials. This means that each individual lamp group or assembly will require an earth connection to the chassis. It is not uncommon for such connections to be connected together at a junction box, and then a single connection to chassis. If this chassis connection fails then all lights could fail or behave abnormally.
Try observing the rear with a direction indicator working (ignition needs to be on). Do the the red tail lights illuminate? If yes then that suggests a faulty earth connection as hinted at by @kik in post #2.

 

[AndyRKett]

Just to add to the posts above agree with everything said.

You can test if its an earth problem but taking a light out of the van but leaving the wiring connected. usually the black will be earth. Disconnect it and make sure the connection is all nice and clean with an old nail file or bit of folded sand paper. Plug it back in. If that doesn't work you can run a bit of wire between a metal part of the car body or chassis, and the earth in the light unit.

If you have a multi meter then this will make testing a lot easier as you could just put the black lead of the meter on the chassis and the red can be used to probe the pins in the plug for the back light to see if there is any power there,