Mechanics

BRAND NEW ALTERNATOR DOES NOT HOLD CHARGE

Ford F-150

Hi guys, props for this site. Amazing. Anyways I own a F-150 1987 4x4 302 5.0L, 4-speed standard, 275 000 kms with rebuilt engine and tranny. Recently my charging system has started acting up and won't hold any charge. I automaticaly assumed it was my alternator as my headlights were dimming up with the RPM speed before the problem occured. I put a brand new one in, changed my regulator and alt. Harness, changed my battery terminals, recharged my battery to about 12.4V, and the altenator still won't charge. It is pretty obvious then that it is a short, isn't it?
I took my truck to the mechanic this morning to get the battery tested, after a few tests, the guy told me it could be the alternator that could be faulthy otherwise it would probably cost me big time to locate that short in order to get it fixed.
Anyways, do you have any heads up to give me, can I locate the short myself or should I just leave it to them. If you do think it's possible, what tools do I need, etc.
Thank you so much, hopefully you can help me save some big bucks that I don't have!
Avatar
Troestler
July 23, 2006.




Not sure I am buying the short idea. Usually when things short, fuses blow, and if its between the battery and the altenator it should be easy to find.

Let me ask you this. Is your Charge Indicator in the instrument panel showing a no charge indication? I guess it is a light on if not charging, and off if charging.

I good test is to check your battery voltage while not connected. Connect the battery with all lights off and the ignition switch off. Does the battery voltage go down? If yes, find out what is drawing current. Maybe a glove box light, or something. Another way to find out what is drawing down is pull fuses to eliminate circuits. Make sure you have a detailed map of which fuses go where before pulling more than one.

Ok, if the voltage stays the same, start the vehicle and see what the voltage is on the battery with the altenator running. I know before you said you changed both the altenator and the regulator, but why did you change the alt harness? Was something bad, corroded, or burnt?

My fist thought is like the mechanics of the altenator or regulator. You might want to trace back the ground for the regulator and see if it is sound. The diagram shows a radio noise capacitor at the ground. Maybe that had gone bad. Just trying to through some ideas your way.
Good luck and let us know what fixes it.

Tiny
Mikeybdman
Jul 23, 2006.
Battery takes no charge? Or does it die off after a few days? Will the truck run all day if you start it? If the charging system has issues, the battery can only run the vehicle until not enough voltage left to power. If the charging system is good, and the battery is shot, will continue to run until shut off, if not enough juice can be put in the battery, will not start without jump
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Tiny
TaurusWheel
Jul 24, 2006.

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