With original voltage 12 V these lamps produce just 5 W of light. These lights in 2008 model year cars with ENS motor code show the index at night. According to law, you should ensure for Jeep Wrangler normal work of light over license plate. The lamps of this type are usually small and non powerful for Jeep with engine volume at 4.0. One suitable for Wrangler type of bulb base is SV8.5-8. One more thing - Jeep Wrangler 4.0 needs only high quality optical devices.
If there are problems with 2008 Jeep Wrangler in index plate light, go to the service. Look out when you relieve old lamp in Jeep and install new W2.1x9.5d bulb. More than 12 V of voltage and different capacity from 5 W will cause problems. You need to have skills and tools for cars with motor S01 having the volume of 4.0. You might have problems with Jeep Wrangler during installing lamps.