Some of you may have read my previous thread where I had some work done on my truck and they came up with a huge list of problems. One of them was the charging system. Truck died when the battery finnaly gave up as it was not getting recharged from the alt. I had the Alt bench tested and it tested fine. I bought a new battery but it still wasnt working charging. The dealer said the alternator was no good, only putting out like 10 volts. So I bought a new alternator...still not charging and no output from the alt. Figured I had a dud froom the parts store, brought it back and got another...still not charging.

SO I got a copy of the ford service manual and after looking at the diagnostic steps there is no way you could have come up with the conclusion of a bad alt by following the steps. The techs probably threw a meter across the alt and saw battery voltage (which was depleted from driving it to the dealer) and said "bad alternator..$40 please. I could have come to the same conclusion for free.

The service manual has you measure the alt output (Circuit 36)and if it is the same as the battery voltage go to the next test. The next test measures the voltage to the field coil (circuit 35) which should be 12v. Mine reads 4v. So I'm betting my original alternator was probably fine all along.

I guess it partially my fault as well. If I had let them rplace the alternator for $350 they would have stumbled across it anyhow. But I paid them for their diagnostic time. I wanted to avoid getting into the circle of replacing parts without knowing if they were good or bad. Now I have to wait another entire week for them to get it back in. My truck has been down for 3 weeks now and I cant wait another week. I may have to check the wiring on my own.

Sorry, just needed to vent a bit

 

Go to the alternator harness, unplug the connector and do these tests.

Yellow wire battery voltage all the time
green (maybe different color) above 2 volts only with the key on

You will probably find the yellow dead, this runs off a fuse which is probably blown, replace it and let us know.

 

Got this one figured out...I was getting 4v to organge but 1-2v to green as it is supposed to. Still no lalt output. Jumped wire to the starter relay where the orange terminates and the alt kicked in and started charging and the battery light turned off. The harness seems to have developed a case of high resistance. I also noticed that output at the alt was about .5-1 higher than at the starter relay. I plan on replacing that section of harness but and running with the orange wire still jumped for now. Should I put a fuse in that jumped section? Also, can someone lookup the ford part# for that harness section?

Looks like going to the dealer ended up costing me over $300 because I though they had some "special" diagnostic equipment to figure out what was wrong. Took me 20 minure swith a voltmeter and service manual. I think from now on I'm going back to always trying to fix it myself first.

 

Getting the factory service publications on any vehicle pays for itself the first time out.

Hootbro

 

Have you try to take the alternator to another auto parts store.... Something simular happen to me with my cadillac. The alternator was not charging. So I took it to my local Oreilly part store and it was tested and it was bad So I bought a new one.

I had the new one installed and it still was not charging. Took it back, they bench test it and it was only putting out 12 volts. So they gave me a new one. I installed it and still bad. took it back and they test it too. same thing... 12 volts and that the diode was bad. It would work and quit working durning the test... So they tested 2 more they had in stock and there were all bad. So they say they must got a bad bach of alternators. They called another O reailly and they tested 3 of them they were bad too. They called another store and they had good alternators. Whew..... Now thats customer service instead of having me going all over the city trying to find a good one.


A little off topic here... From the first store they had a part guy who was testing my return alts trying to say the alts were good and my cadillac had a short somewhere... the alts were putting out 12 volts. Another part guy say if the alts are putting out 12 volts, the alt wouldn't be able to keep up with the headlamps, ac, radio and the computers. He said it should be putting out 14.5 volts..... The first guy was quite.... lets say.... hes not there no more

 

Check the harness where it pass's the battery tray, I had one the other day that had battery acid damaged wiring to the alternator.

 

I pulled out the entire section of harness and everything looks fine. No breaks or kinks. Both fusible links look good. I'm guessing the wires may have some corrosion going on. When I replace that section of harness I'll check the resistance between new and old. Now I'm wondering if the "bad" field coil on the AC they diagnosed is really just the harness because it also connects to the compressor.

No need to take the altenator anywhere...it's working fine with the harness jumped. IT also bench tested fine before I left the parts store

rwillmo, sounds like you've been down this road before...thanks for the tips

 

Concentrate on the orange wire, there should be a connector near the battery, make sure its clean and in good condition, pull test the orange wire and see if breaks under moderate pressure. You should be able to repair that harness no problem. When you find the connector make sure that you have battery voltage at the truck half of the harness, the problem could be farther up the line.

 

the organge wire follows the yellow main alternator wire to the starter relay. Are you talking about the connector between the battery and the vacuum tank? I think the green wire that goes to the battery light might go through that connector

 

Sorry it seems I gave you some miss information. I thought your truck was the same as my 04. Anyway the schematic shows a brown wire feeding a fuse link that then comes out as the orange/light blue, I suspect that this link is mid harness somewhere. Pull on the link and see if it breaks. Most of the time when a link fails it does not break the insulation. Let me know if this helps.

 

This link is actually at the end of the harness near the starter relay. I'll give it the pull test tonight.

 

The schematic shows a double fuse link to the main charge cable and a separate link to the orange as I described above. This does not mean that the schematic is correct. Take a look and let me know.

 

The main yellow positive cable and the orange wire to the ALt plug go into the harness and come out together near the starter relay. There is a fusible link on the orange as it comes out of the harness. The other side of the link is brown and meets up again with the yellow cable where both are spliced to another fusible link. The other side of that link is white with a ring terminal that bolts to the hot side of the starter relay. I'll get some pics tommorow and post em

 

Thats sound about right, give that link and wiring a good pull and let me know.