there is no way the wire from the "rear demister blower" will carry the current load for 2amps
sorry not the fan supply, the heater supply, the read demister blower unit has two supplies, one for the fan and a second larger one for the heater element, this is fused at 30A and is quite a large guage wire it appears to be larger than 14AWG.
I have been quite happily doing it for three years running the infinity Amp you see. its powerful enough to shake and rattle the boot and plenty loud in the car.
The switch is the factory fitted relay system and the only mod was to short out the micro switch as the fan is designed to only work with the roof up.
Yes i do agree if you want to start running stupidly large amps then this is not suitable, but if the lad just wants to stick a sub in then its fine so long as you dont mind loosing the rear demister it also means no requirement to run power cables/fuses etc from the battery (in the front in a cab) to the boot.
as for the power into the boot, following my set up there are a few holes in the two fire walls behind the rear seat. If you remove the rear seat back and boot carpet it wil be obvious (you need to do this anyway to get access to the rear demister. dont forget to protect and live wires with additional insulation where they pass through the boot firewall/metal to avoid rubbing and eventually shorting out. the factory wiring to the rear demister unit has a female/male plug, the wires you need are the larger of the four, red/black one as +12V and the brown is 0V/ground, i simply found another plug from an auto factors, soldered it onto my power leads and plugged it in.
job jobbed
mrlee