You're over thinking this a lot. When the engine is cold, check the voltage of the battery. A fully charged battery will give you a 12.6V or higher reading. Start the engine. Voltage should initially drop and then climb. You should have a minimum voltage of 13.8 and max at 14.2 after a minute or two. The issue with mine was the alternator was only putting out 12.2 volts and that was sporadic. That's not enough to keep a battery alive. When you replace the alternator, which is an easy fix, use ONLY a NEW alternator, NEVER a rebuilt. The rebuilders replace only the parts required to make the unit charge. They do not test or replace the finals that keeps the battery from draining back thru the alternator to ground which is a common defect on Ford systems.

 

OK.... Lets see. Let me say this 1st: Unless you absolutely know what you are doing, NEVER use the ohms or amps scale of the meter anytime you are going to touch a meter lead to any live voltage source. It can damage / destroy the meter. On live circuits, always use the appropriate voltage scales of a greater scale than the anticipated voltage. IE: If testing for 12 VDC, the next highest voltage scale is usually 20 VDC. If in doubt use a higher scale and reduce it till the reading is within range.

This holds true also when checking the alternator housing to ground on a running engine, because if there is a grounding issue, there may very well be voltage present between the test points. When you introduce the meter (on volts scale) across a wire path, the voltage will take the path of least resistance. If a voltage shows on the meter across what should be an unbroken path, that shows there is a problem / resistance in that path and the meter is the path of least resistance. Not good.

Use the following method for checking "Voltage Drop", which is a very accurate way of checking things.

Also, make 100% sure the battery terminals are clean and tight. If any doubt at all, clean and tighten them. 75% of battery / charging problems are caused by crappy battery terminal connections.

1st: Set the meter to DC volts (usually 20 VDC scale) and connect the METER's black negetive lead to battery negetive terminal and the meters red positive lead to the big output wire on the alternator. That'll show the output of the alternator. should be between 13.8 VDC and 14.5 VDC at 2,000 rpm and headlights on. This voltage should be the exact same voltage as the battery voltage. If it isn't, there is a wiring / connection problem.

2nd: While still on DC volts, connect the meter's black negetive lead to the battery positive terminal. Then connect the meters red positive lead to output of the alternator. This is called measuring "voltage drop". If there is any indication of voltage there, there is a bad connection somewhere between the alternator output and the battery positive terminal.

3rd: With the meter still on DC volts, connect the black negative lead of the meter to the battery negetive and meter red positive to the alternator housing. This is called measuring "voltage drop". If there is any voltage measured at all, then you have a bad ground somewhere between the alternator housing and the battery negetive cable.

The slight split in the insulation, in itself, won't be a problem. Wrap some plastic tape around it if it bothers you. Unless of course, the split was caused from the wire overheating and cooking the insulation, usually caused from a bad battery connection. Using the methods I described will tell you if the wire is bad if it "drops voltage" (shows a reading on the volts scale, indicating resistance). Zero volts (voltage drop) from one end of a wire to the other means zero resistance.

PS: If these instructions don't make sense, let me know and I can try to clarify as best I can. Sometimes it's difficult to explain technical things to a novice (which it seems you are) over the computer. If I were you, I would pick up a repair manual for your truck. Even a cheapie generic Haynes manual will explain basic electrical troubleshooting to a degree.

PSS: Incase you are wondering, I owned a highly reputable and sucessful electrical shop specializing in automotive / RV / marine electrical systems for 15 years before severe back problems forced me to sell the business and move on to other things.

 

Labnerd is right on the money!

Simple drop test to check potential in the circuit. I pull the ground on the battery when checking output on the alt.

I have had 2 remanded alternators bad out of the box from auto parts retailers. One on my mustang started to smoke internally the same day it was installed.

 

First off thanks for all your help, very appreciated. I think I'm getting closer to solving this issue.

Question- does the engine have to be on for test #2 and #3?

For test #1 I got 13.54 and compared it to the battery (engine on and revved) I got 13.45.
Not exact but close, significant? What does it mean if it doesn't reach 13.8? I had the alternator bench tested, and had a new one put in and still the check charging system light came on. Maybe they're both bad alternators?

For test #2 I got 0.00 with engine off and 0.12 with engine on and revved, but slowly went down to about .07, maybe it would have went to zero if I kept revving..

For test #3 I got 0 with engine off and .01 with engine on and revved, but went down to zero after a few seconds..

 

Your results for test #1 definitely indicate a problem. That difference is significant.

 

Lemme see... Let me first state that all meters have an accuracy tollerance level listed, usually around + or - .5% on the cheaper ones and that tightens up with quality of the meter, so consider this in your reading results.

Answer to 1st question: All readings are done with engine running, giving you a true life condition. Be carefuly of the rotating parts and fan belt. (Discalimer: These tests should be done by a professional if you question your abilities.)

Test 1 results: The differance between 13.54 and 13.45 volts is on 0.09 volts and can be attributed to be withing the tollerance rating of the meter or a slightly crappy connection between the meter lead and terminal. I would say it's within the margin of error to be expected.

As far as your alternator output voltage is concerned, I would say it is very low. This may be from a bad alternator, bad regulator, a bad belt (slipping), a weak battery, a bad / dirty battery terminal / connection or some huge power draw on the system, but at 2000 RPM, the alternator should be pumping max output. Rated output in the book for these alternators is 13.5 to 15 VDC. At 13.54 VDC, yours is just barely minimum allowable, or marginal at best. The bench testers aren't spot on 100% of the time. All things considered and everything else checks out, I would personally be considering an alternator replacement soon. Remember when I stated 75% of all battery problems are dirty / bad connections? Did you clean the battery posts and clamps and re-instal tightly? If you did, then see the other possible failure points listed above.

Test 2 results: I would clean all connections on the +DC wires. There shouldn't be any indication of voltage there. This shows a resistance connection somewhere in the line. It is low, but can increase with heat.

Test 3 results: Your results are minimal and not out of line. I would still clean / tighten all ground connections.

On a side note, the alternator in my '04 F150 let go last year. Didn't know it had a problem until I was on highway driving home on Christmas Eve last year with lights on, heater blaring (it was freezing out there) and stereo blasting away. After about 30 minutes, "Check Charging System" warning came on. CRAP.... I switched to towing mode (to increase RPM), turned off heater and stereo and in 3-5 minutes warning went away. Turned heater back on and 3 minutes later, warning came back. Turned heater off again. Warning came back at every stop light and went away within 2 minutes of leaving the stop light and made it home. Checked everything out and she was puting out 13.45 VDC at 2000 RPM with headlights on. Turned on heater and voltage began to slowly creap down until warning came on. Changed alternator and problem gone since. Don't forget, when cruising around in overdrive, you are no where near the 2,000 RPM standard for the alternator to be puting out 100% capacity.

 

I suggest not running multiple posts for the same problem. Becomes very confusing for those trying to help you.

https://www.f150online.com/forums/20...-alt-good.html

 

+1 You've spent enough time ****ing around with it and the age of the alternator warrants a change.

 

looking into the issue now myself, apparently the system is running on the battery not the alternator causing the fault light.
the ault is charging at the 13.8 and the battery is holding the charge.
so the system is running all power from the battery.
how to check
disconnect the battery will shut the truck down yes?
meaning its not the charging circuit at fault its the running circuit of the alternator or a bad ault.
?