Wig-Wag Diagram

If you want alternating lights, just add another relay into the circuit after the flasher,but befor the relays (it could even be a two-way flasher). I have no way of drawing it, but basically, you make the flasher control the relay coil, then take your 12V source on pin 30. Output to one light would be 87, the other 87a. Granted, you'ld still have to use the relays configured like in Chase's diagram if you want the lights to work NORMAL too. This is just something I thought of "on-the-spot", so it's never been tested or anything. But I don't see why it wouldn't work.