alternator not charging

Is there anyone out there that can help diagnose a 95 Range Rover 4.0L bad charging system??? I have this Rover that was towed into my auto shop and am not sure where to troubleshoot. The problem is that the alternator is not charging the battery sufficiently. I have done all the basic testing and checks. I installed a new Interstate battery which test good. The alternator is new and bench tested to specifications. At idle the alternator is regulating battery voltage at about 13.0V-12.8 with no accessories on. When I put a 200 amp load on the battery the battery voltage drops to 12.6V-12.4V. I understand the Becm controls the field side of the alternator. Is the Becm bad or should I look for poor connections somewhere? Please help!!!

cmarr

I found the problem! Upon research I found that there were four grounds that needed to be inspected and cleaned. One ground came from the negative battery cable and grounded to the alternator bracket. The other three grounds were near the fuse box under the hood, on the right front fender. I cleaned all these grounds and the alternator charged to specifications. If you ever have any odd electrical problems consider checking these grounds.