Good evening,
I am currently fitting (or trying to fit) LED indicators to my 1985 90.
Fitting them wasn’t an issue, all connections soldered and heat shrinked, but on trying them I have all 4 flashing, I have replaced the standard flasher unit with a LED one and adjusted it so the trailer light doesn’t show.
I wondered if the dash panel bulb might have been an issue so I tried removing that, no difference, there were no issues with the standard 12v bulb indicators (so no signs of earth faults).

Any suggestions welcome
Thanks in advance

I'd say the quickest thing might simply be try a second flasher relay? Unlikely, but if it's faulty you won't fix it otherwise.
Have you tried adjusting the pot fully both ways? May be that you can get them to flash properly, but without the trailer light at a different setting?
Finally, maybe it's because of you vehicle being a bit older the circuit is different? There's a guy here with the same problem on his bike, but then removing the dash bulb should sort that.

Flasher relay is the quickest check.

Also, check this guy out, it's a 1984 model 90:
https://forums.lr4x4.com/topic/91851-led-indicators-fitting-wiring-problems/

He makes the point that because LEDs consume so little current, any earthing problems AT ALL - that is, even a slight earth leak, could screw it all up.

Have you towing electrics?

change tele tale bulb in dash for one that has an earth £22 ebay boltonbits