Electrical

Check the under bonnet fuse box for water damage or loose connections then It's time to get the body systems interface unit scanned,
everything electrical runs through it or is controlled by it.

What is the body interface

Short answer?
it controls every thing,
You indicate left the stalk switch sends a signal to the body systems interface and it's the BSI that actually sends power to the indicator lights,
The same is true with just about every electrical function on the van..
including when it starts and stops the engine.
And they don't like getting water inside them or high voltage arcs from incorrect jump starting,
If it were to come in to me my procedure would be to plug Citroen Lexia diagnostic scan system into it and run a global scan.
This runs a test on every electric module in the vehicle for stored fault codes.
And depending on the result if the BSI is definitely faulty I'd send it of for testing/repair to one of the specialists like "BBA REMAN".
You can't just fit a used one as they're coded to the vehicle.
But if the scan shows up no stored fault codes then it's hunt the wiring fault time,
As stated in my previous post I'd concentrate on the under bonnet fuse box,
another thing that really doesn't like water.
But scan it first,
and I'd really only trust Citroen Lexia diagnostics to do this.
You might just be better calling in an autospark,
The hazards are not meant to have any control over engine running so it's either the BSI or a short circuit somewhere.

Hazards come on their own and multi function relay under bonnet brown keeps buzzing