In late 2001 the car computer was ready for daily use. Still, it was only a matter of time before some changes would have to be made. That time came sooner than I expected.


After having driven it for 6 years, my old 1976 Buick Century bit the dust, in the summer of 2002. Rather than starting a new project for the 1997 Pontiac Bonneville, I kept the same computer and reused some of the car stereo components.

Car Stereo:

Prior to moving the system to my Pontiac Bonneville, I took the opportunity to address some problems that I encountered in my previous install:

In addition there were some other things to account for when moving the car stereo system:


Speaker Boxes:

With no good place on the back deck to mount the subwoofers, a pair of speaker enclosures needed to be built. The design needed to meet the following requirements:

With that in mind I climbed in the trunk and took some measurements. I measured the angle of the back seat, which turned out to be 66 degrees. To avoid blocking the pass-through, the speaker boxes couldn't be any wider than 14 inches. The maximum height measured in at 14 inches.

To avoid nasty resonance problems I didn't want any of the dimensions to be identical. Also, I wanted a little bit of fudge factor when it came to height. For those reasons I changed the height dimension to 13 inches.

[Car Speaker Diagram]With the height, and front angle determined I found a javascipt-based speaker calculation page and start playing with the numbers. In the end, I decided on a trapezoid-shaped enclosure with the following dimensions: 13"H x 14"W x 15.25" D1 x 21"D2.

[Speaker Box under Construction] [Speaker Box with Insulation]
[Finished Speaker Box - Front] [Finished Speaker Box - Back]


Power Wire:

To power the computer, I ran 4 gauge wire direct from the battery to a distribution block in the trunk. To prevent fires and other mishaps an inline fuse holder was added, near the battery.

[Power Wire at Battery] [Power Wire under Hood]

Then at the distribution block power is sent to the power amp and the computer. A relay was used to switch the computer on and off with the vehicle's ignition.

Turn-on wires:

Two remote turn-on wires were run. The first wire was run from the red "12V Switched" wire on the CD Player's wiring harness to the relay on the car computer. This wire is live when the car's ignition is turned on, but dead when the car is turned off. The wire doesn't need to be as heavy as the main power wire, because it's only used to trip the relay coil. This coil consumes a small amount of current. I used 18 gauge wire for this.

The second wire was run from the "power antenna" lead on the CD Player to the power amplifier's "remote turn-on" input. It's live when the CD Player is turned on, and is used to turn the power amp on and off. Since this wire only carries a small amount of current, 18 gauge wire was sufficient.

[Wires Under Back Seat] [Wires routed to trunk]


[Completed OBD-II Box] [OBD-II Box Under Contruction] I ordered an OBD-II interface from in the summer of 2002. The package included a interface board, a 25pin-to-9pin serial cable, and a J1962M connector. At the time, didn't include pre-made cables, so I had to make my own using the J1962M connecter, some data cable, and a 9-pin connector. Since that time, they've made things easier by including pre-made OBD-II cables with their OBD-II kits. No case was included with this kit, but a quick trip to a local Radio Shack store took care of that. The OBD-II interface was mounted inside the dash.

OBD-II Cables:

The ELMScan VPW interface board has two connectors: a DB9M, and a DB25F. The "DB9F to J1962M" cable is used to connect the interface board to the car's OBD-II port. Then a "DB25M to DB9F" serial cable connects the interface board to a standard 9-pin serial port. Last, but not least, I made a "DB9M to DB9F" serial extension cable, and ran it to the trunk. This extension cable is identical to the LCD Serial Cable that I made when I first started this project.

Last Update: 12-28-2006