i had same thing on my fiesta the toher day.... alternator light came on.... wipers, windows, lights were all very dim or slow or not working at all, stereo wouldnt turn on... if i revved it made it worse.... it was the alternator that was fooked. new one and it was right as rain! Remember, just because its new doesnt mean its faulty! I cant see how diesel could cause electric problems your describing... it might run a bit rough but it wouldnt cause alternator light to come on, or the slow elctrics :/ Alternator, Battery or other Electric Fault imo.. Iddy, try putting battery on charge for an hour... if this solves your problem clearly your alternator!