I ordered a new H4 headlight assembly for my Dyna. It has four wires. Blue, green, white, and a yellow. I called J&P and they were no help. My existing light has 3 wires. Ground, high, and low. Is the yellow wire something that is needed since I'm switching from a sealed halogen to an H4?

 

If the new headlight didn't come with a wiring diagram, there's no way of knowing for sure if the wire colors correspond to the same colors in your old harness. It should be pretty simple to open the old and new cans and look at which wire goes where. The 4th wire may be nothing more than a unneeded ground for the can.

 

Prolly a ground for each circuit.

 

Hook up the three that make the light work on high and low and tape off the forth !