The Invisible Audio Upgrade

Created: 4/11/2001

Last updated:

Author/source: Peter Lucas

I have a long-term project to equip my DeLorean with a complete, computerized vehicle monitoring/automation/entertainment system. In doing so, my goal is to change the "look and feel" of the vehicle as little as possible. Part of the fun is to find unused nooks and crannies in the vehicle in which to hide the technology. The following is a photo essay on how I invisibly upgraded my sound system. My primary goal was to add the ability to patch external audio from a computer (e.g., for playing MP3s) into the vehicle's sound system, but in the process I also produced a substantial improvement in the stock radio's sound quality, all without changing the vehicle's interior appearance in any way.

The idea was to install a 4 channel power amplifier between the audio outputs of the radio and the car's four speakers. Many aftermarket car power amps (such as the Pioneer model GMX334 that I used) include speaker level inputs for this purpose in addition to line level inputs. But, since a good amp is pretty large, where to hide it?  After failing to squeeze it under the dashboard, or under the seats, or anywhere else inside the cabin, I finally turned to a somewhat non obvious space: under the spare tire!  It turns out that there is plenty of room for even a fairly hefty amp centered beneath the hub of the spare.

This means getting quite a few wires from the cargo area into the passenger compartment. To be specific, I needed

6 wires (size 16 AWG)  -- from the radio speaker outputs to the amp's speaker level inputs (4 signal plus front and rear neutral)
6 wires (size 16 AWG)  -- from the amp back to the speakers (same as above)
2 wires (size 10 AWG)  -- power and ground for the amp
1 wire (size 16 AWG)   -- "switched" 12V to turn amp on and off
4 mini coax cables        -- line-in from computer to amp

To deal with all of this, I built a custom wire harness that looked like this:

(click to enlarge)

With a little patience and a lot of black electrical tape it is quite easy to make a very professional looking wire harness that looks like it came with the car.

The various wires  need to go to four distinct destinations within the vehicle, each requiring a different length:
1) The single ground wire (black) headed for a convenient chassis ground point below the brake master cylinder. This wire is 20" long.
2) The single power wire (red) goes directly to the battery (through an in-line 30 amp fuse). Length: 110".
3) The speaker in/out wires and the remote power line need to go to the back of the radio under the dash. Length: 66".
4) The 4 "line input" wires terminate in the small storage area behind the drivers seat (which is where my computer will eventually reside). Length: 110"

(Note: Lengths given are approximate--my notes are vague. If you try this, best double-check).

To route the harness from the spare tire well to the passenger cabin without doing too much violence, I used wide metallic tape to produce a flat area near the amp end of the harness. Essentially, I created a short section of ribbon cable. It looks like this:

(click to enlarge)

This permits the wires to exit the luggage area without cutting a hole. The trick is to capture the flat area between the bottom of the spare wheel well and the fuel pump access cover, like this:

(click to enlarge)

When you tighten down the access screws, the foam gasket around the cover will hold and seal the wire nicely (it may be a good idea to put an extra layer of thin foam on either side of the cable to even things out). Since the cover extends under the spare tire, this technique also gets the cables safely out from under the tire.

I did drill one hole in order to get the cable (all except the ground wire, which I terminated with an eyelet connector and grounded in the front ground point below the master cylinder) into the passenger compartment. By drilling a hole of appropriate size directly below the large seal where the heater hoses enter the cabin, you will find yourself with a path to a point high up in the passenger's foot well area, where nobody will ever see. Sealed with an appropriate gasket material, the point of entry looks like this:

(click to enlarge)

I ran the power wire through the center console to the battery compartment and connected it through the 30 amp fuse to the battery + terminal.
The speaker in/out wires plus the +12 switched line were routed under the console to the back of the radio. To make the radio connections, I purchased a short harness with connectors matching those of the standard Craig radio. This part is available from the Mid-State DeLorean Club ( You cut 6 of the 9 wires in order to form a "T" adapter, like this:

(click to enlarge)

Here are the pinouts of the cable from the Craig radio:

Brown -- Left Rear +
Blue    -- Right Common
White   -- Right Rear +
Green  -- Left Front +
Purple  --Left Common
Gray    -- Right Front +
Red      -- +12V Unswitched
Orange -- +12V Switched
Black   -- Ground

(N.B.: -- these color codes are those of the harness coming from the Craig radio, not those of the adapter harness, which are not the same).

The amp control wire gets connected to the pink wire that comes directly out of the radio and goes to the power antenna relay.

Finally, I ran the coaxial input cables through the center console to the locked storage compartment behind the driver's seat. I terminated them in a little panel with four RCA jacks, into which I will plug in my car computer.  It looks like this:

(click to enlarge)

After putting everything together, here's what the amp looks like:

(click to enlarge)

The spare fits nicely over it, the radio sounds great, I have my extra inputs, and no one is the wiser.

Now, if only I can find someplace to stash a subwoofer...

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