Triumph Speedtriple

Have you tried swapping the new bulbs around to see if it’s still the same side affected?

 

Didnt that bike do that as standard and you could buy an upgrade from square deals to make them both come on at once?

 

https://www.squaredeals-ltd.co.uk/h...our-4--other-triumph-models-1xpair-2009-p.asp

 

It sounds very strange that it’s all ok with the original bulbs but not with LEDs. Could it be a bad connection with the new LED on the side that goes out?

 

Be useful if you add the info on your model/year
From avatar it looks like 99-01 Speed Triple

Whether flash to pass or hi off hi/low switch both circuits are identical in regard powering the lamps high beam lamps
One difference however is that with the 'flash' switch, if it is already on low beam, it will actually flash the High beams without actually turning off the low! (with incandescents this means that all 4 filaments would actually be on - with LEDs there are usually just additional elements added)
So you may be confused as to whether it is really working properly with the flash, as what you are probably seeing is the one lamp just remaining on low, while the second is truly going 'high'.

The way the lighting circuits work on that generation (and indeed the next gen) is that the hi/low switch powers ONE lamp directly (opposite lamps for high and low) and the alternative lamp low/high are powered respectively via a headlight relay (again that would be opposite lamp elements for each function)
If ONE of the lamps is NOT coming on in high beam, it pretty much HAS to be the high beam relay.
Be careful when replacing - those headlight relays are not 'typical' convention of most common or garden std relays; they have the common and the coil positive terminal in swapped locations; if you replace with a 'std' relay all will appear to function correctly however the relay coil will be energized all the time, even with ignition off - the headlight will be off, but because the relay is energized, if the bike is not ridden for several days (or not on a battery tender) it will discharge the battery.

 

As an alternative, for £45 each you can get a pair of Wisamic LED lights which fit directly to the H4 connections
Wisamic 5-3/4 5.75" LED
https://www.amazon.co.uk/dp/B01EA7U4GS/ref=cm_sw_r_cp_apa_i_zr4kDbPZGG01F

There are different versions but the pair I fitted to my 2010 Speed Triple are fantastic