My battery light comes on and off when ever it wants in my 2003 6.0 sometimes a couple seconds and sometimes a couple minutes it does it at highway speeds and idle battery are only 1 year old and tested out good at autozone so then I took the alternator off and got it tested and it tested good but I still have an intermitten battery light please help scared I am going to fry my FICM

 

Battery light is pretty much right. I would clean and tighten the battery cables and then charge and load test the batteries. Be sure to disconnect one of the cables as a good battery will cover up for a bad one. Also give the wiring a good once over especially the plug and main cable connections on the back of the alternator. If they're ok, it's going to be the Alternator. Rebuilds and even new from Ford don't have a great batting average. I would check the phone book for a local rebuilder, odds of only fixing it once are much better and save a few bucks in the process. Even better yet is a DC Power Alt if the budget allows. They are expensive but have a great reputation around here.

 

Check your grounds. If all are good my vote is the alternator. Diodes can be self healing once cooled off. I've had a couple of alternators check good on the bench or once cooled down and were bad. If it was my truck I'd spend the money and get a DC alternator if the truck is out of warranty.

 

had same issue on 01 excursion. ended up being wiring harness on back of alternator. been working great. try getting someone to wiggle wires to see if it comes on and off.

 

Good point, as stated check wiring first. I stated grounds because they have been major problems in the past. Esp. if the trucks been worked on.

 

mine was very sensitive. the motor running would cause enough vibrations to make it come on and off, sometimes it would stay on for a while and others it would flicker on and off.

 

Another Vote here For DC Power

https://www.dcpowerinc.com/

My stereo would eat OEM Alternators

No problem with DC power I even tried to trickle charge my batterys the other day the charger just kept turning off So the DC Power alternator is on top of things

they are Brand New Units with NO core to send

Then get a ScanGaugeII to watch things with

 

I am going to get the 185 amp alternator i was wondering if I needed the wire upgrade or would my stock wires be able to handle the extra power

 

They recomend the Wire upgrade I got the Basic upgrade here it is

You can Make your Own but it need a Fuse in it

Mine has a Fusable Link its the Grey wire that connects to the red you can see in the Pics. I got the wire upgrade for free.

But you can just make your own wire upgrade and get Better wire than mine for cheaper










Here is Some more

Ford Truck Enthusiasts Forums - BLADE35's Albums

 

Just fyi....69cj recommends checking grounds.....years ago i had a starting issue....did everything to no avail. I found the ground on the bavk of the engine loose! Very loose.....check them all

 

I was having the same issue. Turns out I had a bad battery. Also caused my ficm to go out.

 

Well I will jump on the bandwagon here. Mine was acting exactly like yours last year. I monitored voltage for about a month before buying the DC Power alternator. Never wouldn't start and always kept batteries charged but I could tell it was just a matter of time before it left me stranded or burned out the FICM. Zero charging issues since.

 

I have an '04 F350 that I have been struggling with this same since Jan.

1. Installed new or probably rebuilt alt from Brand X, upsized to the 140 amp unit in Jan. when the light came on the first time. It has 110K on it so I just figured it was time.
2. I have 1 year old batt's correct for vehicle - Interstate brand.
3. No starting issues, lights work fine, even when towing trailers at night.
4. Dashawk gauge tells me that it is always at 13.2 and higher voltage, even when the dash light is on.
5. I replaced the plug on the alt to wire harness to see if it was the plug.
6. Battery connections are clean and tight.
7. Any grounds I found were tight under the hood.

I had the system checked to see if alt was bad at Brand X, they are telling me all is good, both batteries and alt. The dash light was even going on and off during the test. What I dont get is how they would be able to test the dash light when they are only testing at the battery connections during the test.

Brand X - has a blue and yellow car in Nascar

I am leaning towards the fact that the signal from the alt to the dash light is messed up???? How does one check that?

I searched around multiple sites and couldnt find any wiring diagrams for this circuit to see what triggers the light in the dash. Does the FICM, or other module monitor this? Is it recorded anywhere?

Thanks for any assistance.

'77

 

https://www.ford-trucks.com/forums/m...0&ref=gnr-next

I'm not sure if the link above will work but it's a schematic for single alternator. You can chase this stuff in circles but odds are good it's your alternator. I would load test batteries (seperately) first though.

 

Checking Ripple Voltage
Ripple voltage or (AC voltage) can be measured by switching your DMM to AC and connecting the black lead to a good ground and the red lead to the "BAT" terminal on the back of the alternator, (not at the battery). A good alternator should measure less than .5 VAC with the engine running. A higher reading indicates damaged alternator diodes.

Alternator Leakage Current To check alternator diode leakage, connect the multimeter in series with the alternator output terminal when the car is not running. Leakage current should be a couple of milliamps at most; more often, it will be on the order of 0.5 milliamps. Use care when disconnecting the alternator output wire; make sure the battery is disconnected first.