I have an ex MOD 90 with a 2.5 N/A diesel engine in it. I towed a Brian James car trailer loaded with another 90 on it a few years back. It did it but it was the hardest bit of towing I'd ever done, I only went 40 miles but it felt like double...
Everything (indicator) runs through the hazard switch in the lower dash, everything.
Have you changed the switch (as @tottot said in post #2) they cost less than £10
[part # YUF101490]
I had exactly the same issue, I put it down to a faulty relay socket as I swapped the relay and it still did it. I knew when I had a problem as the glow plug light never came on and the temperature gauge went straight to the red, even though it...
It could be sucking in water through the air filter. Check the air filter box and there should be an outlet pipe with a valve on it to let water out, check this isn't blocked.