Okay, lemme get this out of the way...
'90 Aerostar, 3.0 auto 101k miles...

okay... this truck is driving me nuts... I was told when I bought it that the alternator was toast. I hooked up a tester and it read battery volts before I started the engine and after. No change. okay, i figured this guy was right, so tonight I swapped it out. Hooked up the tester again and still no change when the truck is running. hrmmm... battery terminals clean, alternator plugs clean, belt tension good, battery is new, truck starts and runs with no probs, and battery light is NOT on.

I found a post about the 2 fuse links, and I'm going to go check that now.

any other suggestions?

 

The fusible link to check is "K". The links are attached to one pole of the starter relay on the driver's side fender apron. you are looking for a GREEN fusible link, with a YELLOW wire on one side and a BLACK/ORANGE wire on the other.

 

Go to your local auto parts store and have them test the starting and cargeing circuits. Your home tools are not accurate enough, and don't test for the correct things. Voltage is like a measure of electrical pressure. It tells you nothing about total electrical flow. Not haveing the system tested (which is free by the way), could be costly, as you go through a cycle of replaceing alternators and batteries. The problem could be internal corrosion of the cables. In any case, get the system tested.

 

i dunno... a snap-on DVOM with amp probe is quite accurate... doesn't give me any probs @ work...

okay... fusible links are intact. I talked to a buddy of mine today (driveability tech @ the Ford dearlership i used to work at). He said it could also be something wrong with the gauge, BUT the guage is reading the same as my DVOM and my load tester... I think I'm going to yank it and get it tested independently...

any other suggestions?

 

I don't know much about alternators but I was reading a web page and one of the things it said was:

"One final thing to check - the field voltage. In order for the alternator to generate electricity it must be supplied with a field voltage. If you know which wire is the one that supplies the field (normally labeled 'F') then simply check with a voltmeter to see if there is 12 volts at the field. Another check is to use a hacksaw blade or a lightweight screwdriver , anything magnetic, and hold it near the side of the alternator with the ignition switch turned in the on position. If there is a field voltage present then the metal will be attracted magnetically to the side of the alternator, not very strongly, but you will feel it pull the metal to the side of the alternator."
http://www.misterfixit.com/alterntr.htm

 

also check fuse link C brown, blk/orange 12v wire in and yellow/wht wire out to regulator and field in alternator

from Ford Aero Service CD
i can't post the descriptive pictures from the cd manual

Field Circuit Drain

Connect the voltmeter negative lead to the generator (GEN) (10346) rear housing for all of the following voltage readings:

1. With ignition switch turned to OFF position, contact voltmeter positive lead to voltage regulator (VR) (10316) F terminal screw. The meter should indicate battery voltage if system is operating normally. If less than battery voltage is indicated, proceed with Step 2 to find cause of current drain.

2. Measure voltage at I terminal (ignition switch OFF). If voltage is indicated, service I circuit from ignition switch to eliminate voltage source.

3. If no voltage was indicated in Step 2, contact voltmeter positive lead to wiring plug S terminal. No voltage should be indicated. If no voltage is indicated, replace the voltage regulator.

4. If voltage was indicated in Step 3, disconnect the one pin S terminal connector. Again, contact voltmeter positive (+) lead to voltage regulator wiring plug S terminal. If voltage is indicated, service S lead wiring to eliminate voltage source. If no short is found, replace generator assembly.

 

I'm going to try the last post... but what I have right now: There are 2 plastic plugs in the Alt. 1 plug has 2 black/orange wires & they both read battery voltage. the 3rd wire is white/black, and ohms out good to the the same wire on the other plug. the other 2 wires in the other plug are yellow/white which has battery voltage and the last one is green/red which goes to the indicator in the dash. All these readings seem right... gawd this is driving me nuts....

Rick

 

how about grounding of alternator back to battery? is it good?

 

good question... answer: i dunno... I don't see the ground wire on the schematic, just the symbol on the alt itself... where does it hook up?

 

Just guessing, but it might use the metal thing that it's mounted to as a ground. As you may know, the vehicles metal frame and every thing connected too it (by metal) is electrically connected to the batteries negative battery terminal (ground). So pretty much your entire car is a ground and is grounded unless it's somehow electrically isolated. I believe some foreign cars have their positive and negatives reversed (positive ground but that doesn’t apply here). Try checking the continuity between the case of the alternator and the negative battery terminal. I believe it should read zero ohms. It wouldn’t hurt to disconnect your battery first. I wouldn’t want you to fry your ohm meter because I gave you incorrect advice. Measure to the negative wire that attaches to your battery, instead of the battery itself once it’s disconnected.

 

Do you have the Analog dash or the Digital? I have heard from Ford Mechanics that the Digital causes a lot of problems.

I know it's not always good for the car but my Dad always pulls the battery cable loose to check the Alt./Charging Circuit If it stays running it's good if it dies it's Bad.

JaY

 

Well, I feel I'm going to get some static for saying this, but.....
1. The arc from taking a battery connection off could cause the battery to blow up in your face. 2. The counter emf (electromagnetic force) could cause your car's electronics to fry. (This is one reason Ford puts a damper diode in the starter solenoid switch on your later vehicles) 3. It could ruin the voltage regulator in your alternator. 4. This may or may not tell you if your alternator works. On an old generator system it might, just not not necessarily with an alternator.
Okay, let the static begin.

 

No Static from this corner kruse you're spot in right.

I put 2 re-man ECMs in a customer ride because he did that since his batt would always be low & he kept "Checking his alt" [yeah right, gotcha. let me go throw my digi VOM away]. Spikes & deficits kill digital components. I don't care who says what!

Batt stayed low because he used to leave the door open so he could hear tunes, that + the interior light being on all day kept batt low, sometimes it wouldn't crank over. And then alt got so hot it smelled like hot metal, he went through them also. Some folks are a trip. . . .

He wouldn't believe me whenever I told him it was him, not his vehicle causing it all.

FBp

 

amprobe will not work on dc car system. Voltage test isn't perfect but usually quite adequate.

ken

 

okay... i bit the bullet and took the first alternator back to where I got it... Autozone said "good", OReillys (sp) on the other hand said it was only throwing out 10V... got the replacement this afternoon @ about 4:30 and tossed it in... same prob... so after much moaning and complaining, I listened to my wife and pulled it out... guess what? same problem, only throwing out 10v. I have another coming in the morning...

let me say one thing, I've had nothing but good experiences with OR... and i also didn't but reman alternators, I went with the new stuff.... so.... keep me in your prayers, this truck has to get me to Charlotte NC by Sunday evening...

Rick