Flashing taillights from Amazon.

[Dave Rocks]

I use this light. Got it last June so its been rained on many times. Works great and drivers acknowledge it.

OTYTY Bike Tail Light with Turn Signals, USB Rechargeable Ultra Bright LED Safety Warning Bike Rear Lights, Wireless Remote Control, 4 Modes, Waterproof...​

OTYTY Rear Bike Light

 

[Dave Rocks]

I also have these Bar End Light Plugs mounted into my Handlebar Extender: Bicycle Handlebar Lights 2 Modes Turn Signal Indicator & Safety Warning Light