So, they both run on normal speed when you short the left relay? The right relay isn't used on normal speed, so you could even disconnect that relay and they should still both work on normal speed. This shows that the left relay isn't being energised.
Have you checked all the fuses under the steering wheel? I can't remember which fuse it is, but worth making sure none of them are burnt out.
Also, ceck that you have continuity from pin 2 on the left relay to a pin on the bitron connector. I think it's pin 1, but check them all and if you don't have continuity on any of them then you've got a break in the wire coming out of left relay, pin 2.
If you have continuity from left relay to bitron, and the fuses are all good, then it looks like there's a break between pin 1 of left relay and the fuse.
Working out where the break is, is a tad tricky. First thing is to figure out if the break is in the fan cowling or on the car side. If you undo the fan cowling loom connector, you'll be able to test continuity from the left relay to the pins in the loom connector, fan cowling side. I did this and had to take the fan cowling off the car, but you may be able to do it with the front of the car still attached.
If there is continuity from the relay to the loom connector you know the break is on the car side, not in the cowling.