Thanks found the connection up by the wiper motor tucked away out of sight. (and oversprayed by the PO's repaint)  Reworked things and turn signals all work again. Not sure why I care- no one else uses them around here.   :-)
Kim

Clean the socket the bulb fits into, including the contact at the bottom.

if you can reach the wiring for the lights , then you could connect a test light or meter to verify there is power getting to the rear. There are the connections for the rear wiring harness above the wiper motor then the wires go up the A post to the rear. It could be something came undone at this connecting point.  

850 Mk1 Left rear turn signal is out.  previously worked. Left front is fine, right side is fine, little light on the end of the stalk is fine, so it is not the flasher.  Changed bulb with known good. Tailight/brake lights work so ground is good. Housing is a replacement so not cruddy.   Examined connector from signal bulb  to loom green/red.  Likely suspect is therefore the connection where the green/red from the front meets the green/red from the rear.
So wiring diagram tells me this exists but it is not obvious where? Looked where I suspect it should be - either under dash by steering column or by fuses/ turn signal flasher on the right side of engine compartment and it didn't pop out immediately.  So dumb question of the day is: Where in the rats nest should it be so I can focus my efforts?    All current work has been under the hood so I probably bumped something there....
Thanxs
Kim
PS - new water pump, hoses and radiator  have worked wonders on engine temp- also discovered fan was installed backwards by prior owner- good thing as we are supposed to hit 90 this weekend.....