When talking about headlights for the XJ, the first thing to discuss is their wiring because no matter what your question/concern is, if your headlights are still being powered by the factory wiring, you should change that. In the factory configuration, power for your headlights travels from the battery, through the power distribusion center (PDC) in the engine bay, to the switch in your dash, and then back up to the headlights. This is a problem for two reasons:

• All of the power your lights will use has to pass through your headlight switch. This often leads to damage/melting of the headlight switch and sometimes can even start a fire especially if you're using bulbs that are a higher wattage than stock.
• Voltage drop. As energy passes through wire and switches, voltage is lost. What begins as 12 volts at your battery becomes significantly less by the time it reaches your headlights. Small gauge wire exacerbates the problem of voltage drop, and the factory headlight wiring is quite small. A 10% drop in voltage (a little more than 1 volt) reduces headlight output to 2/3 of its maximum potential!

You remedy this with a relay harness. A relay is essentially a switch that is operated electrically instead of physically. A relay harness allows you to power your headlights directly from your battery and with much thicker wire at the same time rendering voltage drop and potential damage to your headlight switch a thing of the past. Putco's H4 relay harness is quite popular and can be found for less than $30. It's quality isn't top-notch, but it does the job. I use one myself. Many other options exist such as Painless, ARB, Daniel Stern, etc. You can even make your own (instructions found HERE). No modification to your XJ is necessary. The harness attaches to your battery or PDC for power, plugs into your stock headlight plugs, and plugs into your headlights. No cutting. No splicing. You will see a dramatic improvement in lighting even with your stock headlights with nothing more than a relay harness, and even if you want to upgrade your headlights, the relay harness is mandatory if you want to actually see any improvement, so DO IT FIRST.