Is there an easy way to check out the alternator on this engine -  I believe it has a V-6 - the guy went to Sears and they gave him a slip saying "excessive voltage drop" "charging system inoperative"

I'm going over in a bit with my tools and multimeter to check it out.

The Ford integrated regulator alternators had a real problem for a while with the connector which would get dirty where the contact is made , bad connection would then melt the connector or worse.  I had to replace mine once and the parts store actually stocked a replacement pigtail with connector just for that reason.

Hopefully that's the problem or somethig else simple.

The 'battery' light is intermittently going on, and the stereo cuts out when it does.

Advice anyone?  This guy is working two jobs and going to school, has neither spare time nor spare money.

Go start your truck.  With it running, disconnect your positive battery cable from your battery.  If the truck dies, you need an alternator.

Measuring the battery voltage with your multimeter should immediately tell you whether the alternator is supplying a charge. If the voltage with the engine running is well above 12.7 (like somewhere between 13.6 and 14.2 volts), then the alternator is charging. If it's less (essentially the same as it would be with the engine turned off), then either the alternator or the connections between it and the battery is bad.

Bad idea. Without a battery as a load, the voltage will soar, probably frying the engine computer or other electronics.

While you are at it, clean the posts and check the water level in the batteries (if it is not a maintiance free type).

Diddo with what Skibane said.  If voltage is in that 13.6-14.6 (or higher), the alt is working.  

I agree...if the alternator is charging you should measure about 12 volts on the battery with the engine off and something higher (13-14) with the engine running.

If you don't measure this then you need to get somebody to diagnose your problem, I'd hate to see you buy a new alternator only to find out the connections/ cables were bad.

Hmm...

Does your explorer have a voltmeter on the dash? If so, turn your key to 'on', but don't start up. Note the voltage. Then start up, and if the voltmeter moves up when the engine is running (it should drop back when you turn over the engine), your alternator is ok.

And figure out what size engine you have... Counting spark wires is the easiest way...

An alternator can charge yet have low capacity.  Pretty common and also easy to check.

Determine voltage, engine off.

Start and determine voltage with all accessories OFF.

Turn on headlites, stereo, AC fan.  Check voltage.  Should equal no load (running) or very near.  If not, check connections.  If that does not reveal anything, remove alternator for bench check.

Thanks, guys.  I just got back.  

The connectors ("F"? and "A-S-I") at the alternator were dry and some of the blades had a bit of white stuff on them, couldn't be sure if is was corrosion or dried up dielectric grease.

Base voltage with engine off was 12.5 volts.
Idling, it rose to 14.5

Turning on heater, headlights (brights), radio, flashers, brake lights, everything I could think of, we were able to maintain that voltage at 2000 rpm.

I did one other test -  with the "F" screw grounded, a jumper from "A" connector to "A" blade, the "S" and "I" voltages (idling) were
in the proper 2:1 ratio.

Talking to the owner, he said that the problem was occurring after sitting overnight, but then after running an hour or so, there would be no problem with the light coming on or the stereo cutting out.

We cleaned the connectors thoroughly, then put all kinds of silicon dielectric grease on the blades and on the the connectors.  Also around the outside of the connectors, to help keep dirt & moisture out.

We'll see how it goes over the next couple of days.  The replacement alternator was $130 rebuilt to $150 new, and it was getting late & dark, so lacking evidence that the alternator was really bad, we decided not to rush to the store to buy something expensive that he probably doesn't need.

Did you make sure that they battery is charged/good?  Alternators need voltage to get energized to put out power.

You gotta love problems that come and go..... they're the worst to fix too.

 

I knew I left something out.  The battery is less than 4 months old and stays very well charged.  Its just that the intermittent idiot light and power interruption on the stereo was causing concern.