2000 D2
1. Fuses are all fine
2. PO installed a trailer light package on it.
3. No tail lights!
Is there a lucas ground wire that can cause the tail lights not to function?
1971 Rolls you turned on the wiper motor and the radio turned off then back on (ground)

 

I have seen a lot of bad aftermarket wiring. The trailer light setup may be a good place to start. Check all the connections very closely for loose or disconnected wires and possible corrosion. Whenever I have a wiring job come in to the shop, the aftermarket stuff is the first place I look for problems.

Beyond that, have you taken the light assemblies out to check for corrosion, bad bulbs, etc.? I would take the bulbs out and check for corrosion in the bulb sockets and check the bulbs with an ohm meter. If they don't look corroded and the bulbs are good, I would check for 12v coming in to the connector at the lights. If you have power there, then check the grounds.

I had a problem with one of my tail lights a few years ago. It ended up being corrosion. I don't remember exactly what was corroded, but I cleaned it up and got it working until I got a new one. If I remember right, the lens had leaked and let water in.