Hi guys, i searched and couldnt find an answer. I was looking for the normal voltage output of an alternator at idle with no accessories on and with accessories on. When i start my truck it's putting out 14.1 volts. Then as i drive along it drops to 13.7. This is with no accessories running. When i turn the lights on etc, heater its putting out anywhere from 13.5 to 13.1 volts. tonight i even seen it dip down to 12.8 then went back up to 13.5 with the lights on etc. Any ideas?
truck is 1996 f250. 460 cc 4x4

 

my father in laws ( master mechanic ) test for alternators is as follows :
pull up to your garage door or a wall , turn on the headlights with car running , then start turning on everything , ie. fans , blinkers , wipers , and see if the lights dim , if they are dimming then the alternator is not keeping up with demand. No test gauge required

 

Your truck should have a 3G alternator in it from the factory. It is a pretty stout piece. In my opinion yours is on the weak side. Pull it out then have it tested.

 

That would be true for most systems but I can tell you my '92 F350 has the poorly designed 2G alternator in it. It works to specification, but exhibits the exact symptoms you listed above. I could swap in a dozen 2G's and still have the same problem.

When I get my 3G from RJM Technologies I'll let you know if my truck passes the test!