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Battery Power For (Eg) Subwoofer Amp


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I mentioned in another thread an alternative power source to get a 10 amp plus feed for things like underseat subwoofers. I've got some pics together so I thought I'd post them up as a separate thread.

This was done on a 2011 Aygo.

There is a fuse - 40A HTR - at back of the instrument panel fed from the Battery (via other fuses, but always live). This uses a black cable to feed the HTR Relay contact, which when made feeds the 7.5A A/C fuse at the side of the instruments. I didn't find the HTR Relay but identified the black cable out of the fuse and teed into that 40A feed. This saves having to get a cable into the engine bay and safely routed to and connected to the Battery, but is is a slight fiddly job - fat hands won't help.

To start disconnect the Battery. Remove the speedo pod cowl (screw each side of column). Remove the two screws at the bottom of the speedo assembly and lift the unit up to get it off it's bracket. Turn it to the left a bit to get behind and you can see this:


The 40A HTR fuse is buried in the middle - inside the purple circle above. The cable you want is is in the plug nearby along with red, blue and white/black wires - all heavy ones - see green circle above.

Pull this plug out (I pulled the one next out first to make it easier) and swing it round so you can get at the wires. There is another black cable in a plug higher up - that is not the cable you're looking for!

There isn't a lot of slack, but my method is not to cut these cables, so even if my joint fails at some stage the original power feed will remain intact. To do this I carefully cut round the insulation with a sharp knife in two places, make a lengthways cut between them and then peel off that section of plastic:


Then I strip the end of my T cable - in this case it's the yellow power feed for a Pioneer powered sub - and wrap it securely round the bared section:


In the background you can now see the inline fuse that comes with the Pioneer wiring.

Then I solder it:


Obviously if you can't solder you will struggle with this, but it only takes a few seconds so if you can find a pal who can they could do this quite quickly.

Then I wrap the joint with insulating tape and finish it with a cable tie. The latter is partly to take the strain off the joint (it's at the two wire end) but mainly to ensure the tape doesn't unravel as I've found some lose their stick after a few years.


Pop the plugs back in. Tidy up your new cable and clip/tape/tie it on it's way to where it's going. Refit speedo and cowl. Do rest of job ...

On a slightly different point I was aware that the radio can be used without the key in the ignition (once only for 30 mins) so wanted the sub to be 'on' then as well as in normal use. To achieve this the control wire for the sub would need to be controlled by the headunit rather than just ign/acc, but none of the wires out of the stock radio did this. However I found a terminal on the unused socket on the headunit that did do this, so I soldered the sub control wire direct to this as below:


The pic isn't very clear I'm afraid, but the pin is in the middle row (of 3). I put heatshrink on the surrounding pins first to ensure no stray strands could short, and afterwards I blobbed some 5 min epoxy in around those pins to reinforce the joint mechanically. (Just out of picture the wire goes into one of those bayonet inline fuses which provides a disconnect so the unit can still be removed.)

This terminal is live when the radio is on with the key off or out, and also when the key is in acc or ign position (oddly even if the radio is off).

Incidentally, in the Ice version with 6 Speakers the 'rear' Speakers (in the doors) are the outer pin pairs in the white plug, which I teed into (again just out of shot). The inner pins are the front Speakers, and in the black plug below are the power wires.

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