I've got one of those battery charging issues that is about as much fun as getting a root canal.

My battery charge light will occasionally light at a cold start up. Volts show just under 12v and stay there. If I shut down in a few minutes, it seems to "reset" and everything goes back to normal: no light and volts head up to 13v and more as the batteries recover from the start, the volts eventually settle around 14v. This happens without any type of frequency or pattern (such as only when cold outside or after sitting for a few days, etc).

Any thoughts? Bad alternator (it's only about 30 months old and not much mileage/hours)? Batts are also 30 months old. Voltage regulator? 7th Fetzer valve? It's all ball bearing nowadays...

Any advice and help is much appreciated!

 

be sure to get that muck out of there!

xtof

 

Bueller? Bueller? Anyone? Anyone?

 

My first thought would be to determine if the battery light is really indicating a problem, but you already did that by observing the low voltage when the light was on.

If you have a single alternator (and if there aren't too many changes between by 99 diagram and your 02 truck), I would guess that either the alternator is intermittent or there is a problem with fuse # 6 (10 A) in the power distribution box, which supplies field current to the alternator.

I'm assuming that the belt is tight and all of your electrical connections are clean and tight.

Chris

 

Thanks Chris. All of your assumptions are correct (single alternator, new serpentine belt and even replaced the tensioner pulley at that time, electrical connections are clean as far as I know, but with so many, who knows??).

I will check that fuse when my wife gets back from showing off in the beast this evening. Any thoughts about a control module or sticky relay somewhere?

Thank you!

 

The alternator field fuse (# 6) gets its power directly from the battery through a fuse link, and the alternator output goes directly to the battery through a separate fuse link, so it doesn't look like there are any relays.

The only control electronics would be the rectifier diodes and voltage regulator built into the alternator. I'm not sure if the voltage regulator is individually servicable, but I doubt it, and rectifier diodes almost never fail intermittently.

Here is the charging system page from my 1999 wiring diagram:



As long as the color code hasn't changed it should help you trace out the wires when you check the connections.

Chris

 

Newer alternator notwithstanding - the internal regulator sounds bad. How are you at replacing regulators?

 

Thanks everyone. Turned out to be a(nother) bad alternator. A few tools, 30 minutes, and $240 to replace it. One worthy note: I replaced with a Motorcraft brand from the dealer. I had an aftermarket brand on there (starts with a "N" and ends with a "A" and has a "AP" in the middle). I will let readers know over time if the more expensive Ford product holds out longer.

A second note (and plug for Isspro gauges): I am glad I took the time years ago and installed a voltmeter from Isspro. It was key to helping diagnose the problem. If you need a reason to backup the idiot light, this would be a good one.

 

Glad you got it fixed. Keeping your eye on an accurate voltmeter goes a long way toward identifying electrical problems before they leave you stranded. Now if only they would bring ammeters back.