The symptom:
The left hand side external indicator lights, front rear & repeater, not working.
The instrument dash panel warning light flashed and the sounder operated at the correct speed.
The lamp (bulb is something that grows in the garden!) failure waning light was not illuminated.

I changed the body processor module BPM behind glove box; No change
I changed the lamp control module LCM in the boot/trunk; No change

With the LHS indicator switched on I removed the fuse in the LHS heel board fuse box. This caused the warning light and sounder to speed up indicating a lamp failure and the lamp failure warning light illuminated. With the fuse removed there was a constant 12V supply to one side of the fuse.

This implied that the wiring to all external lights was intact with no break of circuit.
This was proven later.

The problem was therefore between the BPM and the LCM. The plug/sockets to the LCM above the fuel tank and below the LHS front heater vent were checked and sprayed with contact cleaner; No change.

The BPM provides the switching for the flashing by grounding/earthing an output from the lamp control processor. There are two wires that run from the LCM to the BPM. Yellow with blue trace for RHS, Yellow with slate trace for LHS.

If these are grounded/earthed from the LCM the external lights will illuminate permanently. This is replicating the function of the BPM without the flashing function.

I swapped the two yellow wires round and the LHS indicators functioned correctly when the switch was put into the RH turn position. This proved where the fault was.

I then looped the Yellow/Slate wire from the LCM to FC5 the multi pin plug socket below the LHS front heater vent. The left hand indicators then functioned correctly.

There was a break in the wire between the BPM and the LCM.

I then looped from the LCM to the multi pin plug/socket above the fuel tank BT4. The left hand indicators then functioned correctly. There was a break in the wire within the boot/trunk. I cut the Yellow/Slate wire at the LCM and the plug/socket and spliced in a new wire.

Result; success everything works correctly!

Thanks to my friend Russell who helped on solving this problem. It took 4 hours!

 

Impressive!

A model of successful troubleshooting (regardless of how long it took). Did you actually find the broken spot, and where was it located?

 

No I didnt bother as the broken wire is now completely out of circuit. I first thought the loom had chaffed through near the boot/trunk lid gas strut but that wasn't the case. The loom is too well wrapped to pull out the offending wire. Best left alone now I feel. Thanks for your comment.