Your obviously not familiar with a 79 Elky taillight. As I've said 2 small 2wire lights ARE the 3rd taillight.I'm still not understanding why you are dead set on using the side marker lights instead of the taillight/brakelight existing wiring... if you use the side markers, you'd still have to run a wire from the brakelight somehow, along with the wiring for the individual turn signals, and wiring for the reverse lights (if you still intend to use them...)