Indicator/Flasher problems

Anybody got advice on how to troubleshoot indicator problems. I have front indicators,left and right,both working properly (and the dash panel light) but not a squeak from either of the back indicators. Ive pulled all the connectors and contact sprayed them,also the switch gear. I swapped the flasher relay for another with the same result. I have a 3 pin relay using the X and L pins. Not obvious damage or significant corrosion on the connectors or wiring.
Any help with this appreciated.
(Its the CSR build (in the signature below) so the wiring harness is a bit of a mongrel with a mix of CSR and ZXR bits.Not a straight forward ' Follow the wiring diagram' job)