Thanks for trying to help Roy..
Well may help others but I was resigned to the fact of having to take back on Monday. Anyway lesson learned, keep persisting and thinking, you may find a solution.
I tried fiddling with blink settings and brightness settings on the 36-566, no joy. Changed chip around, no joy. Checked bulbs. Suddenly one end worked when I put plug back in terminal. Bingo. But other end still no joy. Checked other terminals, Bingo - it had been inserted in the wrong terminal. All working!! Hallelujah!!
I'm presuming the spare terminals can be used for a red tail light, perhaps..?