Installing amplifier/better speakers/under-seat sub

The aim of this upgrade is to approximate FIAT's Interscope system (which I have never seen or heard) by adding (to the standard head unit) improved speakers, an amplifier for the speakers, and an under-seat subwoofer.

I finally reached the stage of hitting the power button this evening - and it all works - wiring up this sound system and sound-deadening one door seems to have taken most of the day :eek: I would have thought only a little simple wiring was needed - an hour's work? - but it seems to take a bit longer than that. Maybe eight hours!

Here are the details for my sound system install, in case they are of interest to anyone attempting something similar. To keep things fairly clear, I'm going to describe each part in a separate message.


Amplifiers should have a direct supply from the battery; there was someone who used the cigarette lighter wire as a power supply with success, but it's best not to, especially if you have two amplifiers. The car's own wiring to that socket is really not very generous and neither is the fuse rating.

On the other hand, there's no need to go over the top for the power supply cable and fuseholder - 8-gauge cable and a 60A glass fuse may seem like a good idea, but they are only really necessary if you have 300W+ of amplifier power (RMS, not peak!), and in the 500, the standard battery and alternator are lightly-rated, so it's probably not the best car for 'dB-drag racing'.

I wanted a standard underbonnet appearance, so I used a sealed fuseholder with regular blade fuse - maximum rating for this type is 40A. The fuseholder has 12-gauge wires attached. I extended one wire to an eye terminal, which is fastened onto a spare stud on the battery positive terminal. For the power cable into the car, I used 10-gauge. Again, this is appropriate for currents up to 40A (4% voltage drop at this maximum current). Expected loading for a 60W RMS/2 channel amp plus 50W RMS/1 channel amp is 14.1A, at which there will be approximately a 1.4% voltage drop. I shall fit a 30A fuse.

I found an unused grommet in an ideal place, under/behind brake pipes on the bulkhead, next to the brake servo. I removed the grommet, cut a hole in it, then used a Philips screwdriver to make a hole through the bulkhead soundproofing (inside the car) - the brown outer layer is surprisingly soft and crumbly, so it is easy to perforate. The cable comes out in a fairly clear area behind the dashboard (left/passenger's side).

The corrugated loom tube provides extra protection against abrasion and runs right through the grommet and inside the car. Helps with the 'standard' appearance; also has red heatshrink applied at intervals to identify as a power cable, which seems to be the done thing these days at FIAT, except they use red insulation tape :eek:

  1. Fuse holder circled in yellow, cap secured by nut that holds ECU onto bracket
  2. Cap again circled in yellow, fuse holder shown removed and 40A fuse installed, also note battery terminal with added wire
  3. Holder clipped into place and battery terminal cover fitted
  4. Grommet and corrugated loom tube through bulkhead - brake servo on right of pic
  5. Cable emerges above brake linkages - needs to be kept clear

The next part explains the installation of the speakers.