Nick,
Here are some picture of the work lights I installed on my JD770. I bought the rear work light from JD. It was about $40 and included a wiring harness that plugged into the existing black connector on the left side of the tractor just behind the seat (see picture).
Since my loader blocks the front lights on the tractor when it is raised up a few feet, I bought a work light for the front too. Instead of buying the expensive JD work light, I bought a Blazer work light from Advanced Auto Parts for $15 and wired it into the existing black connector on the right side of the tractor just behind the seat. I mounted the light up on the ROPS with a piece of metal I bought at Lowes and painted JD green (See picture). I used the existing bolt hole on the ROPS so as not to drill into it.
If these lights burn out, you replace the entire lens. The bulb inside the glass lens is not accessible. The lens pops out of the front of the plastic housing.
Bruce