Would like to get an install heated rear seats for my 97 850 GLT wagon. Is this a difficult and expensive job to retro fit, either to buy the heating pads, switches and wiring harnesses from Volvo, and then tear the leather seats apart and install them. or, to look around and try to find a matching pair in a wrecking yard somewhere? And lastly, will that 100 watt alternator run all four at the same time? Dick