Left or Right makes all indicators flash

This is my first post after learning from other wise owners for a while. Last month the new leased car I had went back at the end of its contract, and now I drive a 1994 Defender 90 CSW as my main vehicle. With 200k on the clock, I gulp at what I've taken on...

Since buying it I've fixed a few things (prop shaft, outrigger fuel tank support, tail electrics) but the indicators have me stumped. I'm sure they were OK until the last thing I did ,which was to put bulbs in where missing in the instrument panel. Now, operating the Left or Right indicator makes all indicators flash.

After studying the wiring diagram in the book, since both indicators light up the same instrument panel light, is it possible for current to leak from the Left indicator side to the Right, THROUGH the instrument panel light? The warning light itself is very faint, after swapping the bulb was still faint. Hazards work OK.

I would appreciate any helpful pointers...

either the wires to each side are shorted or switch is at fault id think

Thanks James. I'll get going with the multimeter tomorrow morning (if it doesn't freeze up) and I'll post back with the results.

I swapped the dashboard indicator bulb and bulbholder with another, which made no difference, then removed it altogether and the problem went away.

It does seem as though one side indicator was powering the other side through the dashboard light, but that makes me wonder how the system normally works without that happening. Anyway, it works for now.