Hi Bill, Slayer61 is on the money with the relay set up however you may find the attached layout easier. You are dealing with small currents so you can simply loop terminals 30 & 87 on the back of the relay. That way the only additional wiring will be the grounds for the relays and looping in the second stop light. There are however a couple of things to look out for
you will need to swop out the flasher relay for one that isn't current sensitive as you are using LED lights (stock autoparts store item for trailer towing etc)
The original stop light was 21w so pulled 1.75amps. Whilst LED's pull smaller current you are now driving two lamps instead of one so it is worth checking how much current they draw together to be sure you don't overload the wiring. If the lamp manufacturer can't give you this information you could hook them up on the bench and measure the current draw with a multimeter.
Hi Bill, a quick update on my last post. Both Slayers and my ideas appear to be flawed. Slayer please correct me if I am reading it wrong but your system appears to only operate they rear lamps (not the front turn signals as well) and appears to be an independent toggle switch, not the original handlebar switch which switches the output from the flasher relay so is not a constant 12v ? Mine will work if you are braking or turning but not both at the same time!
I have an idea of a hybrid of the two which will work from the original handlebar switch but it is late now here in the U.K. so I will put a diagram together tomorrow when I have time to look at the wiring diagram for this bike if you think that would be useful
Ok this one had me scratching my head for a bit, in Europe all turn signals have to be amber so we don't have these combined systems. It can be done but is complex (multiple relays and wiring changes) to work from the factory switch. This made me think how is it done on early American muscle cars?
Good news, if you look at the attached there is an off the shelf solution available in the states for $15 which needs minimal wiring work as it uses the original turn signal and stop light wiring.
PS: you will still need to swop out the mechanical flasher relay as per my original post. Be lucky