If you've ever put a new sound system into your car and been left with a set of old but usable speakers, here's a fun and inexpensive way to project your music out into the parking lot while you're grilling at tailgate events. This is just a quick setup I threw together with random parts in the garage on my 2000 Pontiac Grand Prix, but it ended up working pretty well. With speakers mounted inside the trunk lid, you can just park, open up the trunk, and toggle the radio output to these exterior speakers. Now everyone outside can hear your tunes, not just the 5 people inside the sedan. Keep a cooler and some folding chairs inside the trunk and then you're ready to go!
Step 1: Get Speakers!
First you just need some speakers! Like I said, I just used some old ones that I replaced from stock systems, and they work out fine. Whatever you can dig up will probably be fine, as long as the sound quality is desirable.
Then just work on the layout to make sure that they will fit on the trunk lid so that it can still close properly. I ended up using (3) 6.5" and (2) 4"x6" speakers, and set them up in a line right across the top.
Step 2: Mount the Speakers
I had an old street sign post, and aside from being slightly heavier than necessary, it did a good job of mounting the speakers and making clearance for the magnet up against the trunk lid. I carefully drilled into the portions of the trunk lid where there was elevated metal surfaces(see picture), just make sure not to drill all the way through your trunk! Two sections of signpost secured the tops and bottoms of the speakers, all just using 1/2" bolts. Where necessary, small pieces of wood served as spacers to keep the post even across the lid. Again, just be careful to make sure that the trunk will have clearance to close, and that the speakers won't be crushed or fall off when the lid shuts.
Step 3: Secure Speakers
For the big 6.5" speakers, I found it helpful to add a thin strip of flexible plastic between the two sign posts just to offer a third mounting point for the speaker.
Step 4: Wire It Up
I wired the rear speaker power into the 6.5"s and the front speaker power from the radio into the 4"x6"s just to have more power going back. The rear speakers were easy to access because they were accessible directly inside the trunk. Have the signal wires from the radio go into the switch so that it can be toggled to either the rear speakers or the trunk speakers, so that there isn't constant sound in your trunk.
Step 5: Wire It Up (front Speakers)
Running wires from the front wire signal was a bit more difficult, but worked out pretty well. I just took the radio out and tapped directly into the front speaker wires. I had the wires switched at the front and just ran the wire for the trunk 4"x6" speakers under the molding along the side of the cab and back to the trunk.
Step 6: Switching the Signals
I actually didn't want to run up to RadioShack to buy toggle switches, so I ended up just cutting up some old strands of Christmas lights and used the plugs to switch from one set of speakers to another. I made sure to use the rest of the Christmas lights too for some extra style.
Step 7: Some Finishing Touches
Gotta add a little sign for you and your crew above the speakers for when you have the lid up! Then I added the Bazooka bass tube inside for a little extra kick to shake up the car. I'm also usually a big fan of LEDs, but the Christmas lights ended up having a pretty cool effect too (parallel in sets of 5) for hanging out at night.