I dont know a lot about electrics but if it is the alternator why would it be charging the aux batt and not the crank, to me i would have checked the duel batt set up, but like I said dont know much bout electrics, so would be interesting to know what the prob is and to understand how that could happen as most duel batt set ups should charge the crank batt over the aux. I am just asking for personal interest and not disagreeing with Yendor as He obviously knows what he is talking about and my understanding of it is way off.