CD-RW/DVD: Because every great PC deserves a great optical drive, I installed a LaCie Slim Combo CD-RW/DVD-ROM ($130) in the LCD bracket. This drive is USB2.0, as the distance from the drive is too far for IDE. I fleshed out the LCD bracket with some textured ABS plastic and mounted the drive about where the stock CD player would be. Some might ask why I didn't use a slot-loading drive, and to be honest I just didn't think about it when I bought the drive. I never did like slot-loading CD players anyway. They scratch. It doesn't matter, this combo drive is for installing software, ripping and burning audio CDs and playing DVDs for passengers. It looks good too. The drive plays DVDs just fine on USB, the 1ghz CPU hovers around 50% when playing full-screen DVDs. The only catch was powering the drive. All the devices I have attached to my PC won't allow it to run on bus power alone, so I cut up the AC cable and wired it to the +5V side of a drive connector on the PC. Works like a charm.
OBD II Interface: Keeping tabs on my car's performance and maintence is important for me. It seems silly to have a nice car that you just let waste away. One good tool for checking on your car is OBD II, the diagnostic interface. OBD II manifests itself as a trapezoidal connector under your steering column to which a serial device can be attached to monitor your car's parameters. There are plenty of these devices designed to interface with a PC, but scantool.net sells them for $80 and open-source software is available to display the data it collects. I hooked one of these things up to my car and the results are interesting. I can get speed, RPMs, airflow volume, coolant and intake temps, trouble codes--all of which can be displayed on the LCD in (nearly) real-time. The software from scantool.net is good, but does not like my touchscreen for some unknown reason, so I've been trying the third-party apps available for it and they work well.
Auxillary Battery: Way down in the bowels of this article, I wrote about adding a second battery to my car and I've finally gotten around to connecting it. In the trunk, I installed the auxillary battery inside of a plastic battery box (this is important in the unlikely case of leakage). The battery box is mounted using a piece of plywood about 5/8" thick set UNDERNEATH trunk carpeting and pad. This allows me to screw (1") down through the bottom of the box, holding it fairly securely with no drilling through the trunk or ugly mounts. NAPA Auto Parts supplied all the pieces for connecting the isolator and battery to the existing electricals. I ran 6AWG cable from under the hood through the firewall, left interior molding and into the trunk. AllData DIY said there was a grounding point on the rear luggage shelf for the new battery, but there were no bolts I had nuts for there. I found the thickest piece of sheet metal, ground off the paint and drilled a hole for a bolt I could attach the ground cable to. With some finagling, I attached the battery isolator under to hood according to the wiring diagram provided for my alternator. It's very important to wire a fuse between the terminal under the hood and the second battery. This fuse should be as close to the second battery as possible to prevent a wire that has lost it's insulation from shorting to the body. If this happens and the line is not fused, it will overheat and destroy your battery--maybe even start a fire. Choose a fuse of amperage just above the output rating of your alternator. The last step is attaching the PC and amplifier to the auxillary terminal of the isolator.
Roof Rack: This has nothing to do with computers at all, but I do own a kayak and tend to bring home unwieldy items from Home Depot. I felt it was appropriate that my very functional car have a roof rack. I'm not going to tell you who manufactured my kit. It's very nice and installed easily, but it was expensive to the point of extortion. I even when to so far as to black out the logos plastered all over the plastics, I was so put off by the cost of two fricken bars. I may have undertaken a project to make a rack myself, but that was at the risk of my car's paintjob. I've given this project the nickname "Sport Utility Sedan".