Here's what i did:
Excuse the bad writing, the cat is trying to eat my pencil. Just pick up the left and right turn signals somewhere and couple them thru diodes to one light. Any cheap diode is fine, go to Radio Shack, 1N4001, 4004, etc. Observe polarity: the stripe end of the diode goes toward the bulb. You can use a 12v LED or an incandescent bulb. The LED will last forever.