Has the 4wd ever worked? Could be the chain in the xfer case. What xfer case do you have? I know it might sound stupid but if you just bought this jeep, does it have a front drive shaft?
Do you have any sort of lift? You have a worn out part in the front steering and/or suspension. Check your track bar, ball joints, bushings, and tie rod ends.
the12volt.com is a great site. Do you know what brand speakers are in the soundbar? The 250w is peak power but your aftermarket deck is only putting out maybe 22-25 watts per channel. If you want better sound quality and louder you would need an amp. If you are looking at putting in a sub...
I would try what "TerryMason" suggested and also check the level of your fluid, some ABS lights will come on due to the fluid being to low, my money would be on a dirty or bad wheel speed sensor.
I used LED strips from Ebay for mine and they have been on for about a year now. No issues at all. I have more pics on my personal computer of what they look like from underneath. I am on my work computer now.
I have seen that error come up when speed sensors go bad, there are 2 and when one goes bad the correct signal is not received by the other. Have you tried checking those or replacing those?