Had the same problem. I ordered the kit from Custom Cruisers.co.uk. Having fitted the bulbs and changed the relay, all lights flashed together, and I cut the wires to the indicator lamp on the panel. Customer Cruisers sent this:
The LED flasher kit works well on most of the Triumph model range. Ocasionally we have had this problem, once on a T595, and another time on a Bonnie.
I dont know why it happens on some, but not all Bonnies. I can only assume that the problem might be associated with the warning lamp or how it is wired to each individual bike.
One of my customers cured it by doing this:
"Hi Frank.
As suspected the problem lies with the wiring for the dash
indicator bulb. I have resolved this on my bike by cutting
the wires and adding a full-wave rectifier to the circuit. I
also had to add a 500 OHM resistor in parallel, to one bulb
on each side of the indicators (IE one on the left, one on
the right) to stop a dim flash on the opposite circuit, when
using the indicators (I hope all this makes sense!).
Regards, Phil"
If this sounds a bit complex or if you fail to find a solution we will be happy to refund you for the kit.
Sorry for any inconveniece caused.
Kind regards.
Frank.
At least they tried.