Kev UK,
I don't mean to muddy the water here by butting in with my thoughts. But I'll add ...
Your first entry description sounded very similar to an issue I had with my 1961 Chevy.
I had installed a new steering column and connected the wires incorrectly. My front turn signals worked fine however my rears acted just like your description.
What I found was I had 3 wires connected incorrectly for the rear lights. Your situation sounded very similar to my issue.
I was wondering if your wiring has been redone.
Brian
